LIBRARY   OF 


JOHN    GALEN    HOWARD 


GIFT   OF 


PRACTICAL  CENTRING 


TREATING  OF  THE  PRACTICE  OF 


CENTRING    ARCHES 


In  Building  Construction  as  carried  on  in  the  United 
States  at  the  Present  Time 


ALSO 


GIVING  OTHER  USEFUL  INFORMATION  OF  VALUE 
TO  THE  TRADE 


BY 

OWEN  B.  MAGINNIS 


SIXTY-FIVE    ILLUSTRATIONS 


NEW  YORK 
WILLIAM    T.   COMSTOCK,   PUBLISHER 

No.  23   WARREN   STREET 
1891 


0 

fn 


COPYRIGHT,  1887,  BV 
OWEN  B.   MAGINNIS, 


INTRODUCTION. 


TN  response  to  a  request  from  many  carpenters  and 
±  builders  to  republish  in  book  form  the  following" 
.articles,  which  originally  appeared  in  Carpentry  and  Build- 
ing, The  National  Builder,  and  The  American  Builder,  all 
published  in  the  United  States,  and  in  the  Illustrated 
Carpenter  and  Builder,  published  in  London,  England, 
I  now  take  pleasure  in  putting  forth  this  little  volume, 
with  the  hope  that  they  will  find  it  useful. 

The  work  embraces  each  subject  in  detail,  and  in 
language  that  practical  men  can  understand.  I  would 
especially  commend  it  to  the  attention  of  students 
attending  trade,  technical,  and  architectural  schools, 
as  they  will  find  it  helpful  in  acquiring  the  practical 
knowledge  of  construction  so  essential  to  success. 

My  best  thanks  are  due  to  the  builders,  from  whom 
I  have  obtained  much  of  my  information ;  also  to  the 
publisher,  who  has  gotten  up  the  book  in  a  form  to 
be  a  useful  addition  to  the  chest  or  book-shelf  of  every 
rising  worker  in  the  trade. 

OWEN   B.  MAGINNIS. 

NEW  YORK,  1891. 


CONTENTS. 


CHAPTER  I. 

PAGE 

Practical  Centring. — Centres  of  fireplaces  or  brick  lintels. — 
Centres  for  segmental  arches  of  small  span,  showing 
methods  of  construction 7-12 

CHAPTER  II. 

Segmental  arch  of  4  ft.  span. — Centring  a  semicircular  arch 
of  small  span,  with  methods  of  striking  the  curve  and 
form  of  construction 13-18 

CHAPTER  III. 

Centring  a  brick  opening  of  wide  span. — Striking  out  bear, 
ers  of  frames. — Centres  of  elliptic  arches  up  to  10  ft. 
span. —  Different  methods  of  striking  and  laying  out 
elliptic  curves. — Also  general  construction 19-25 

CHAPTER  IV. 

Centre  for  an  arch  of  16  ft.  span,  constructed  to  sustain 
heavy  stone  voussoirs  in  ashlar  work. — Simple  centres 
for  Gothic  arches,  comprising  the  equilateral,  the 
drop,  the  lancet,  the  three-centre,  and  the  four-centre 
arches 26-32 

CHAPTER  V. 
Centring  circular  windows 33~34 

CHAPTER  VI. 
Suspended  centres 35-37 

CHAPTER  VII. 
Oblique  or  skew  centres 38-41 


6  CONTENTS. 

CHAPTER  VIII. 

PAGE 

Flaring  or  splayed  centres 42-47 

CHAPTER  IX. 
Two  examples  of  centres  suitable  for  wide  spans 48-49 

CHAPTER  X. 
Sewer  centres 50-57 

CHAPTER  XL 
How  to  make  a  diminishing  plumb  rule 58-61 

CHAPTER  XII. 
Trimming  windows  for  shutters 62-64 

CHAPTER  XIII. 
Setting  jambs 65-68 

CHAPTER  XIV. 
Working  hardwood  and  clamping 69-7 1 

CHAPTER  XV. 

Extemporized  scaffolding 72-74 

CHAPTER  XVI. 
Hints  and  suggestions 75-80 


PRACTICAL   CENTRING. 


CHAPTER  I. 

PRACTICAL  CENTRING. CENTRES  OF  FIREPLACES    OR  BRICK  LINTELS. 

CENTRES  FOR  SEGMENTAL    ARCHES    OF    SMALL  SPAN,    SHOWING 

METHODS    OF    CONSTRUCTION. 

/CENTRING  may  be  described  as  an  auxiliary  art 
\_j  employed  by  masons  in  building  construction  for  the 
purpose  of  sustaining  temporarily  the  voussoirs,  or  pieces 
of  stone  or  brick  which  form  an  arch,  holding  them  in  their 
correct  position  until  the  last,  or  keying  piece,  is  inserted,, 
and  the  whole  arch  has  had  time  to  settle  into  place.  The 
temporary  supports  used  are  called  "centres,"  and  are  usu- 
ally supplied  by  the  carpenter.  It  devolves  upon  him  to> 
put  them  in  correct  position  under  the  intended  arch  when- 
ever required  'by  the  mason.  Centres,  accordingly,  must 
be  constructed  of  correct  shape,  and  in  a  way  to  have  suf- 
ficient strength,  both  by  nature  of  the  form  and  the  ma- 
terial employed,  to  resist  the  weight  which  is  to  be  placed 
upon  them.  The  centres  must  be  firmly  fixed  in  place,  and 
yet,  as  they  are  only  for  temporary  use,  provision  must  be 
made  for  gradually  lowering  them  for  the  purpose  of  taking- 
them  out  when  they  have  fulfilled  their  mission.  There 
are  many  kinds  of  centres  required  for  the  different  designs 
of  arches  which  are  constructed,  reaching  from  the  simple 
brick  lintel  to  the  complex  groin.  All  of  these  demand 
care  in  their  design  and  construction. 

In  an  attempt  to  illustrate  principles  and  show  methods 
of  construction  I  will  commence  at  the  simplest  form — 


8 


PRACTICAL  CENTRING. 


namely,  that  which,  is  illustrated  in  Fig.  i  of  the  accom- 
panying sketches.  While  this  example  may  be  considered 
elementary,  and  is  certainly  easy  to  understand,  it,  in  fact, 


SKEV/BACK 


FIG.  I. — Simple  Fireplace. 

involves  the  whole  system  of  centring.  The  view  repre- 
sents an  open  cavity  or  fireplace,  2  ft.  6  in.  wide,  and  3  ft. 
high,  over  which  the  bricklayer  has  to  build  an  arch,  or,  as 
it  is  commonly  called,  "extend  a  brick  lintel."  To  con- 
struct the  centre  necessary  for  this  purpose  the  carpenter 
would  use  first  a  piece  of  ^  in.  pine  somewhat  longer  than 
the  width  of  the  opening  between  the  jambs,  and  would 
joint  one  of  its  edges.  He  would  then  square  across  both 
ends  -^g  in.  shorter  than  the  width  of  the  opening,  and 
draw  a  line  parallel  to  and  i  in.  removed  from  the  jointed 
edge,  all  as  shown  in  Fig.  2  of  the  illustrations.  He  would 
then  divide  the  length  into  two  equal  parts,  and  square 
across  the  division  point.  Then,  laying  the  piece  of  board 


CROV 


FIG.  2. — Getting  the  Curve. 

down  on  the  bench,  and  tacking  it  there,  he  would  drive 
three  nails,  as  shown  in  the  sketch,  one  at  each  springing 
point,  or  where  the  curve  cuts  the  parallel  line  already  re- 
ferred to.  He  would  drive  one  also  at  the  crown  or  middle 
point,  as  indicated.  He  would  then  bend  a  pliable  lath 
around  the  three  nails  and  mark  by  it  the  required  curve  of 


PRACTICAL  CENTRING.  9 

the  arch.  He  would  next  saw  out  clean  this  line,  using  for 
the  purpose  a  compass  saw  or  band  saw,  in  case  the  work 
is  being-  done  where  such  a  machine  is  available.  He 
would  also  saw  across  with  the  square  lines,  and  would 
finally  clean  the  curved  edge  neatly.  By  this  means  the 
mould  would  be  secured  for  the  centre,  or  for  several  cen- 


FIG.  3.— Another  form  of  Centre. 

tres,  if  more  than  one  be  needed.  In  preparing  the  piece 
for  the  centre,  this  mould  would  be  used  on  both  sides  of 
a  piece  of  2  in.  by  4  in.  stuff,  marking  the  desired  shape. 
This  would  then  be  sawed  to  the  line  and  cross-cut  on  the 
square  lines,  resulting  in  the  same  shape  as  the  mould 
already  described.  The  resulting  piece  would  be  the  cen- 
tre on  which  the  arch  would  be  turned,  having  a  rise,  ac- 
cording to  the  conditions  already  mentioned,  of  i  in.  The 
length  of  the  uprights  to  be  used  under  the  arch  would  be 
2  ft.  1 1  in.  This  added,  to  the  thickness  of  the  centre,  i 
in.,  already  mentioned,  would  give  3  ft.  to  the  springing 
line.  Another  form  of  centre  sometimes  employed  is  illus- 
trated in  Fig.  3.  This  is  worked  to  triangular  form,  the 
curve  being  added  by  means  of  mortar  put  in  place  by  the 
mason  as  he  lays  his  brick.  Arches  built  this  way,  how- 
ever, are  not  so  satisfactory  as  when  laid  upon  centres  fin- 
ished to  the  exact  curve  required. 


FIG.  4.— Centre  and  Supporters. 

To  set  the  centre  the  carpenter  would  proceed  as  follows : 
He  would  construct  the  frame  shown  in  Fig.   4  (the  up- 


IO 


PRACTICAL  CENTRING. 


rights  are  i  in.  by  4  in.),  and  would  place  in  the  opening  in 
Fig.  i ,  keeping  the  front  edges  of  the  upright  flush  with 
the  face  of  the  brickwork.  Two  braces  would  be  driven 
in,  as  shown  in  Fig.  4,  between  the  uprights,  to  hold  them 
fast  against  the  jambs.  The  centre  would  then  be  cor- 


FIG.  5. — A  Window  or  Door  Opening. 

rectly  levelled  by  applying  the  spirit  level  to  the  bottom 
side  of  the  centre.  Whichever  side  was  too  low  would  be 
furred  up.  The  mason  would  then  proceed  to  turn  the 
arch,  as  shown  in  Fig.  i.  To  ease  the  centre  the  braces 
would  first  be  gently  knocked  out,  and  then  the  bottom 
ends  of  the  uprights  would  be  forced  outward  from  the 


FIG.  6. — Striking  the  Curve, 

jambs  towards  the  middle  of  the  opening.     By  this  means1 
the  arch  would  be  lowered  uniformly. 

Fig.  5  represents  a  segmental  arch  spanning  a  door  or 
window.     It  may  be  assumed  to  be  2  ft.  8  in.  wide,  with  a 


PRACTICAL  CENTRING. 


I  I 


rise  of  12  in.,  and  the  wall  may  be  assumed  to  be  8  in. 
thick.  To  make  a  centre  of  this  kind  the  carpenter  would 
proceed  as  follows:  A  sound  rough  board  i  in.  thick, 
equal  in  width  to  the  rise — that  is,  12  in. — would  be  used 
in  the  manner  shown  in  Fig.  6.  The  centre  by  which  to 
construct  the  curve  would  be  found  as  shown  to  the  right. 
The  curve  would  be  struck  by  means  of  a  trammel,  or,  in 
the  absence  of  this,  a  rod  would  be  cut  equal  to  the  radius  of 
the  curve.  A  brad  awl  would  be  driven  through  the  cen- 
tre of  the  rod,  a  block  being  placed  under  for  the  purpose 
of  raising  it  up  to  the  thickness  of  the  board,  and  the  curve 
described  as  shown  at  the  left  in  Fig.  6.  The  springing 
line  in  this  case  would  be  2  ft.  6^  in.  long,  or  i^  in.  less 


FIG.  7. — Construction  of  the  Centre. 

than  the  length  of  the  arch,  in  order  to  allow  for  the 
thickness  of  the  battens  forming  the  top  of  the  arch. 
These  would  be  i/%  in.  in  thickness,  and  one  of  them  would 
come  on  each  side,  thus  making  it  necessary  to  allow  twice 
seven-eighths.  After  the  curve  had  been  struck  in  this 
manner  the  carpenter  would  cut  the  piece  out  of  the  board, 
clean  the  curved  edge  neatly  to  the  line,  and,  using  this 
as  a  pattern,  mark  out  as  many  as  might  be  required  for 
the  number  of  arches  to  be  constructed.  A  pair  would  be 
necessary  for  each  centre.  Standing  the  curved  pieces  on 
their  bottom  edges,  as  shown  in  Fig.  7,  parallel  to  each 
other,  and  8  in.  apart,  measuring  between  outside  faces, 
the  workman  would  next  tack  on  three  battens,  as  shown  at 
A,  B,  and  C  in  Fig.  7.  He  would  use  for  this  purpose  8d. 


12  PRACTICAL  CENTRING. 


common  nails.  Then,  commencing  at  point  A,  he  would 
nail  on  the  other  battens,  putting  them  ]/2  in,  apart, 
and  keeping  their  ends  flush  with  the  face  of  the  curved 
pieces,  all  as  indicated  in  Fig.  8.  For  the  purpose  of  ac- 


Fio.  8. — Bottom  View  of  Centre. 


curately  spacing  the  batten,  a  piece  of  J^  in.  stuff  about  10 
in.  long  would  be  used.  Two  cleats  would  also  be  nailed 
.across  the  bottom  edges  of  the  curved  pieces,  as  indicated 
in  Figs.  5  and  8,  their  purpose  being  to  form  a  rest  for  the 


FIG.  9. — Top  View  of  Centre. 

* 

centre  on  the  top  of  the  uprights.  Figs.  8  and  9  show  the 
top  and  bottom  view  of  the  centre,  constructed  as  de- 
scribed, and  indicates  the  position  of  the  uprights  which 
are  used  to  support  it. 


CHAPTER  II. 

SEGMENTAL     ARCH     OF    4    FT.     SPAN.  CENTRING     A     SEMICIRCULAR 

ARCH     OF     SMALL     SPAN,      WITH     METHODS     OF     STRIKING      THE 
CURVE,     AND    FORM    OF    CONSTRUCTION. 

CONTINUING   the    consideration    of    centres   for   sup- 
porting1 segmental  arches  from  3   ft.  span  and   up- 
ward, an  arch  is  shown  at  Fig.  10  turned  on  its  neces- 


FIG.  10. — Simple  Segmental  Arch  with  Centre  in  place. 

sary  centre.     The  construction  of  this  centre  is  a  matter 
of   more   difficulty  and   labor  than  the  two  described  in 


14  PRACTICAL  CENTRING. 

the  last  chapter,  as  there  is  involved  the  principle  of  a 
trussed  frame.  The  centre  is  formed  of  two  frames 
like  that  shown,  the  face  side  at  Fig.  10,  and  the  reverse 
side  at  Fig",  n,  consisting  of  four  pieces  each — namely, 


FIG.  ii. — Elevation  of  Inside  of  Centre. 

two  principal  bearers  curved  on  edge  to  the  required 
arc,  and  two  tie  pieces,  one  across  the  vertical  joint  directly 
under  the  crown  and  key  brick  to  hold  the  bearers  to- 
gether, and  a  tie  or  foot  piece  to  prevent  the  feet  from 
slipping  when  weighted  above.  The  binding  cleats  across 
the  bottom  and  battens  are  as  before  described.  To  con- 
struct this  frame,  which  is  employed  when  the  height  of 
the  arch  to  the  soffit  exceeds  the  width  of  an  ordinary 
board,  it  is  usual  to  describe  the  curve  in  the  same  way  as 
before,  using  a  rod  or  trammel  on  a  drawing  board  or  floor, 
and  to  mark  the  lines  shown  under  the  bevels  as  on  Fig. 


— I — f *" 

V 

FIG.  12. — Method  of  obtaining  Bevels. 

12  in  such  a  manner  that  the  i  in.  board  which  is  suit- 
ably wide  enough  can  be  applied,  taking  care  that  there 
•will  be  enough  stuff  on  to  cut  out  the  curve.  Then  by 
tacking  this  board  to  the  floor,  with  its  bottom  edge  to  the 
indicated  lines,  the  curve  can  be  struck  from  the  centre  A, 
Fig.  12.  Squaring  up  from  the  spring  line  and  from  the 
centre  A,  the  plumb  joint  and  bevel  at  the  crown  will  be 


PRACTICAL  CENTRING.  15 

found,  likewise  the  foot  bevels  can  be  found  on  the  spring 
line.  Fig.  13  is  a  sketch  of  a  board  marked  ready  for 
sawing  out  the  piece.  Care  must  be  taken  to  have  the 
bevelled  butt  joints  and  curved  edges  perfectly  square  from 
the  face,  otherwise  the  whole  construction  will  be  twisted 
and  unfit  to  sustain  an  arch  whose  soffit  is  intended  to  be 
level.  Proceed  to  prepare  the  upper  binding  piece  and 


FIG.  13. — Half  Curve  of  Frame. 

lower  tie,  each  about  3  in.  wide  and  i  in.  thick,  and 
to  nail  them  on  to  the  bearers  after  the  manner  of  Figs.  10 
and  1 1 ,  using  8d.  clinch  nails,  and  turning  their  points 
when  driven  to  insure  a  firm  and  stable  frame ;  also  dress 
off  the  upper  piece  to  the  curve  of  the  bearers.  Construct 
another  similar  frame  to  constitute  a  pair,  and  place  them 
parallel  to  each  other  at  a  distance  apart  equal  to  the  thick- 
ness of  the  intended  arch,  as  shown  at  Fig.  14.  Nail  on 


FIG.  14. — Plan  of  Frame  Centre. 

spaced  battens  and  bottom  cleats,  as  before  illustrated,  and 
the  centre  will  be  complete  and  ready  for  setting  in  posi- 
tion. 

In  order  to  set  this  centre  four  uprights  will  be  necessary, 
one  under  each  corner  of  the  centre  proper  resting  on  thin 
double  wedges  placed  on  a  block,  as  shown  at  Figs.  10  and 
15.  These  are  cut  to  the  height  of  the  spring  line,  less  the 
thickness  of  cross-cleats,  and  are  also  toe-nailed  to  them. 
On  the  opposite  faces  of  the  uprights  cross-blocks  are 
affixed  spanning  the  two  uprights;  between  and  against 
these  blocks  the  required  brace  is  tightly  driven.  By  em- 
ploying cross-blocks  the  necessity  of  using  two  braces  is  ob- 


1 6  PRACTICAL   CENTRING. 

viated,  with  the  same  results,  that  is,  pressing  the  uprights 
firmly  against  the  jambs  by  the  braces  acting  on  the  blocks. 
Should  the  lower  ends  of  the  uprights  spring  out  by  the  pres- 
sure of  the  upper  brace  on  their  middle  part  another  brace 
can  be  placed,  as  indicated.  The  construction  of  the  centre 
proper  is  more  clearly  shown  in  section  at  Fig.  1 5 ,  repre- 
senting as  it  does  the  brick  rowlocks  or  rings  constituting 
the  arch  resting  on  the  battens,  the  battens  on  the  frames, 


FIG.  15. — Section  of  Centre  through  Crown. 

frames  on  cleats,  cleats  on  uprights  and  uprights  on  wedges. 
The  object  in  using  the  latter  under  the  uprights  is  to 
gradually  lower  the  centre  by  allowing  it  to  fall  by  its  own 
weight  from  the  superstructure  above,  so  that  the  different 
brick  may  come  by  degrees  to  their  bearings  without  a  too 
sudden  application  of  the  weight  exerted  on  the  extrados 
or  upper  side  of  the  arch.  It  is  best  to  allow  the  centre  to 
remain  some  time  in  position,  as  removing  it  too  soon  en- 
dangers the  arch,  which  is  never  reliable  until  the  mortar 


PRACTICAL   CENTRING. 


is  thoroughly  set.  Wedges,  therefore,  permit  of  conven- 
ient and  early  easing,  yet  still  keep  the  work  secure.  Fig. 
1 6  represents  the  centre  for  a  semicircular  arch  of  the  same 


FIG.  16. — Centre  of  Horizontal  Arch. 


span  and  character  as  Fig.  10.  It  is  similarly  constructed, 
excepting  as  regards  the  curved  bearers,  each  of  which 
occupies  a  quadrant  of  one-half  the  semicircular  curve, 
Fig.  17.  In  connection  with  this  it  will  be  noticed  that 


FIG.    17.  — Striking  the  Curve. 

when  the  centre  is  a  part  of  a  circle,  a  semicircle,  a  quad- 
rant, etc.,  the  bevels  of  the  bearers  will  be  equal.  In  this 
case  the  bevel  is  an  angle  of  45°,  as  the  bottom  edges  are 

2 


I  8  PRACTICAL    CENTRING. 

the  two  sides  of  a  square.  This  is  also  the  case  with 
centres  when  the  bottom  edges  form  a  semi-hexagon,  semi- 
octagon,  and  so  on  with  all  polygon  figures.  In  setting 


FIG.  18.—  Elevation  of  Inside  of  Centre. 

this  centre  the  same  process  as  has  been  just  described  is 
repeated,  but  if  the  opening  be  low  the  wedges  can  be 
omitted. 


CHAPTER  III. 

CENTRING      A      BRICK      OPENING      OF     WIDE      SPAN.  STRIKING     OUT 

BEARERS     OF     FRAMES. CENTRES    OF    ELLIPTIC    ARCHES    UP    TO 

10    FT.    SPAN. DIFFERENT    METHODS    OF  STRIKING  AND  LAYING 

OUT    ELLIPTIC    CURVES. ALSO    GENERAL    CONSTRUCTION. 

SINCE  the  modern  practice  of  centring  is  based  on  a 
well-tried  system,  it  follows  that  simple  centres  em- 
ployed in  ordinary  construction  are  similar  in  character, 
.and  are  all  planned  in  accordance  with  well-defined  rules. 
The  fact  is  plainly  exemplified  in  Fig.  19  of  the  accom- 
panying- illustrations.  In  this  a  centre  is  constructed  fol- 
lowing the  rules  explained  in  the  last  chapter.  It  is  made 
up  of  three  principal  bearers,  the  outer  edges  of  which  are 
curved  to  the  required  arc.  The  illustration  also  shows 
how  a  semicircular  arch  is  subdivided  into  an  equal  num- 
ber of  parts,  in  which  the  bevels  for  the  butt  joints  are 
always  the  same.  It  is  not,  however,  always  the  case  that 
the  rough  boards  are  of  equal  width.  In  many  instances 
they  are  scrap  stuff,  so  that  the  bevel  shown  in  Fig.  20  can- 
not be  applied.  In  such  cases  it  is  usual  to  lay  out  the 
curve  and  spring  line,  full  size,  on  a  floor.  Divide  the 
curved  line  into  three  equal  spaces,  as  seen  in  Figs.  19  and 
22,  and  draw  lines  to  the  centre  point.  By  placing  the 
rough  boards  over  these  lines,  as  indicated  by  the  dotted 
section  in  Fig.  22,  the  bevel  on  the  butt  joints  can  be  easily 
marked  with  a  pencil  or  knife;  then,  by  sawing  on  the 
mark,  the  joint  will  be  obtained.  The  frame  shown  in  Fig. 
19  is  stiffened  by  broad  tie  battens  nailed  across  the  beveled 
joints,  as  shown  in  Fig.  22  If  the  bearers  be  narrow,  sup- 
porting braces  must  be  nailed  on  the  battens  above  and  the 
tie  piece  running  in  the  direction  of  the  joint  lines,  to  sup- 
port the  joint.  Cross  battens  on  the  top  edges  of  the  curved 


20 


PRACTICAL    CENTRING. 


bearers  may  be  ^  in.  thick,  or  of  any  other  convenient 
thickness,  but  a  thickness  must  be  allowed  for  in  striking- 
the  curves.  The  centre  thus  constructed  is  set  up  as  be- 
fore, placed  on  upright  joists  and  wedges  and  sheathed  in 


FIG.  19. — Wide  Span,  Semicircular  Centre, 

place  between  the  jambs.  In  cheap  work  it  is  not  the  rule 
to  employ  wedges,  but  their  use  is  obvious,  and  therefore 
necessary  for  the  purpose  before  stated.  In  Fig.  23  an- 
other form  of  centre  is  shown,  and  one  that  involves  more 


PRACTICAL    CENTRING. 


21 


FlG,  20. — Striking  out  the  Curves  of  the  Bearers. 


YlG.  21. — Elliptic  Curve  from  Intersecting  Lines. 


FIG.  22.-  Reverse  side  of  Fig.  19 


22 


PRACTICAL   CENTRING. 


skill  and  more  careful  consideration  than  anything  we  have 
so  far  described.  The  centre  is  that  which  would  be  re- 
quired in  building  an  elliptical  stone  arch  of  4  ft.  span.  The 
plan  of  construction  followed  resembles  that  of  the  4  ft.  hori- 
zontal arch  already  referred  to,  but,  inasmuch  as  the  curve 
is  different,  a  different  plan  is  followed,  and  getting  curved. 


FIG.  23.  —  Elliptical  Arch  Centre. 

bearers  requires  more  labor.  There  are  various  methods- 
laid  down  in  the  books  used  by  mechanics  for  sweeping 
elliptical  curves.  A  very  desirable  one  for  general  use  is- 
that  indicated  in  Fig.  24.  The  illustration  referred  to 
shows  an  elliptical  curve  struck  by  means  of  a  sliding  tram- 
mel. As  this  instrument  is  in  daily  use  in  all  shops  of  any 
pretensions  throughout  the  country,  it  is  well  known,  and 


PRACTICAL    CENTRING.  23 

therefore  requires  very  brief  description.  It  consists  of  two 
faX2  in.  grooved  cross  pieces  halved  together.  Slides 
are  provided  in  which  pins  are  inserted.  To  these  pins  a 
trammel  rod  is  fixed  which  works  at  the  required  distance 
necessary  to  trace  the  curve.  The  trammel  is  set  here  as 
in  all  cases — that  is  to  say,  the  distance  from  the  lower  pin 
to  the  tracer  is  equal  to  half  of  the  long  diameter — in  other 
words,  the  spring  line  or  major  axis  of  the  elliptical  arch. 
The  distance  from  the  upper  pin  to  the  tracer  is  equal  to 
half  the  short  diameter  of  the  elliptic  arch  or  its  rise.  The 
curve  shown  is  for  the  bearers  in  Fig.  24,  one  of  which  is 


FIG.  24. — Striking  an  Elliptic  Curve  with  Trammel. 

shown  in  the  left-hand  part  of  the  sketch.  Of  course,  the 
centre  lines  marked  on  the  ends  of  the  trammel  are^placed 
directly  on  the  centre  lines  of  the  draft  board ;  it  is  there 
tacked  fast. 

Fig.  2 1  illustrates  another  common  method  of  striking  an 
elliptical  curve.  It  is  the  method  commonly  known  as  in- 
tersection of  lines.  It  is  not  nearly  so  desirable  for  use  in 
practical  work  as  the  one  illustrated  in  Fig.  24.  The  same 
mode  of  construction  and  setting  as  was  used  in  the  hori- 
zontal arch  is  employed  in  this  case. 

Since  arches  of  wide  span  necessitate  large  voussoirs  to 
resist  the  strain  acting  on  their  extrados,  or  upper  side, 
wide  spans  call  for  larger  centres  and  strong,  reliable  con-  . 


24 


PRACTICAL    CENTRING. 


struction.  The  elliptical  span  gateway  shown  in  Fig.  27 
illustrates  this.  Owing  to  the  size  and  shape  of  the  stones 
employed  in  this  work,  considerable  weight  rests  on  the 
centre  used  for  the  purpose.  There  is  also  another  feature 
connected  with  this  centre  which  must  be  considered  and 
allowed  for.  The  key-stone  projects  i  in.  below  the  face 


FIG.  25. — Reverse  side  of  Fig.  27. 

of  the  soffit.  The  centre  is  therefore  built  in  a  way  to 
make  allowance  for  this.  On  a  clean,  level  floor  the  spring 
line  is  drawn,  as  shown  in  Fig.  26.  Having  an  arch  of  10 
ft.  span,  this  line  would  be  run,  probably,  12  ft.  long. 
A  centre  point  is  established  from  which  a  line  is  drawn, 
square  up,  extending  to  the  height  of  the  rise  of  the  frame, 
in  this  case  i  ft.  5  in.  The  line  is  continued  below  the 


FIG.  26. — Laying  down  an  Elliptical  Frame. 

spring  line,  as  indicated.  The  trammel  is  then  set  as  al- 
ready described,  and  the  elliptical  curve  drawn.  To  find 
the  bevelled  joints  we  divide  the  curve  into  four  equal 
parts,  and  mark  on  the  spring  line  the  distance  from  the 
spring  point  to  the  first  division.  We  join  these  by  a 
straight  line,  which  gives  us  the  direction  of  the  bevel 
joints.  Place  the  rough  boards,  out  of  which  the  centre  is 


PRACTICAL   CENTRING.  25 

to  be  made,  so  that  they  will  be  wide  enough  to  cut  the 
curve  and  mark  them  out,  as  shown  in  the  illustration. 
Cut  out  of  the  middle  piece  a  notch  for  the  key-stone, 
measuring  the  width  on  each  side  of  the  vertical  centre  line. 
This  frame,  like  the  one  shown  in  Fig.  19,  is  stiffened  by 
fattens  resting  on  two  braces,  as  in  Fig.  22.  The  number 
of  the  pieces  is  as  follows:  Curved  bearers  \l/2  in.  thick  by 
12  in.  wide,  tie-piece  2  X6  in.,  battens  across  joints  ij^  X8 


FIG.  27. — Centre  for  an  Elliptical  Gateway. 

in.,  supporting  braces  2X4  in. ;  the  whole  is  firmly  spiked 
together  with  2od.  spikes.  The  top  of  the  centre  is  covered 
with  i  in.  cleats,  spaced  ^  in.  apart.  The  bottom  cleats 
are  2X4  in.,  the  uprights  3X6  in.,  and  the  shore  between 
the  beams  3X6  in.  Great  care  must  be  exercised  in  setting 
a  centre  for  stone  work,  since  different  stones  are  worked 
exactly  to  their  shape  and  size,  and  the  centre  must  be 
perfectly  true,  so  that  the  joints  will  come  right. 


CHAPTER  IV. 

CENTRE    FOR    AN    ARCH    OF    15   FT.  SPAN,   CONSTRUCTED    TO    SUSTAIN 

HEAVY    STONE  VOUSSOIRS    IN    ASHLAR    WORK. SIMPLE   CENTRES- 

FOR      GOTHIC     ARCHES,      COMPRISING      THE      EQUILATERAL,      THE 
'  DROP,      THE      LANCET,      THE     THREE     CENTRE,      AND     THE     FOUR 
CENTRE    ARCHES. 

CONTINUING  the  general  subject  of  Centring,  sev- 
eral illustrations  of  which  are  presented  herewith,  I 
would  first  direct  attention  to  Fig.  28,  which  shows  very 
plainly  the  necessity  of  using  .great  care  and  accuracy  in 
setting  centres  in  order  to  carry  stone  work.  Here  the 
voussoirs  are  cut  to  correspond  with  the  running  courses  of 
ashlar,  and  are  bound  into  the  wall,  thereby  insuring  great 
stability.  The  arch,  16  ft.  in  diameter,  is  sustained  by  a 
framed  centre  constructed  on  the  Howe  principle,  the 
whole  construction  being  placed  in  tension  and  tightened 
by  the  iron  bolt.  The  bolt  A  is  headed  at  the  top  and 
passes  through  the  transverse  piece  B,  the  foot  of  the  brace 
and  tie-piece  C  bringing  the  weight  on  the  bearer  joints  D 
D  entirely  on  the  centre  of  the  longitudinal  tie-piece  E'. 
This  is  suspended  on  A  passing  through  B.  B  is  supported 
by  the  braces  F  F,  which  rest  on  the  tie-piece  E.  The 
weight,  being  carried  on  the  uprights,  rests  solidly  on  the 
stone  sill  below.  On  the  lower  side  of  the  tie-piece  is 
shown  how  the  bearer  joints  are  all  similar,  the  inside  fig- 
ure being  an  octagon  and  the  bevels  G  G  being  set  to  the 
same  angle.  The  curve  of  the  centre  is  carried  below  the 
centre  line  or  diameter.  This  is  done  for  architectural 
effect;  hence,  the  spring  line  must  be  indicated  and  the 
bearers  must  be  laid  out  from  it ;  all  lines  below  must  be 
drawn  parallel  to  it.  The  timber  used  in  the  construction 
of  centres  of  large  diameter  must  be  sound  in  character  and 


PRACTICAL   CENTRING.  2/ 

of  large  dimensions.  The  tie-piece  in  this  case  is  2  X  8 
in.,  braced  with  2X8  in.,  halved  together  in  crossing, 
and  joggled  into  the  tie-piece.  The  braces  should  not  be 
less  than  i%  in.  thick,  and  should  be  as  wide  as  pos- 
sible. The  bearers  should  be  2  in.  thick;  the  trans- 
verse piece  B  should  be  3X6  in.;  the  wrought-iron  rod 
should  be  i  in.  in  diameter.  Since  the  stones  weigh  a 


FIG.  28. — Large  Centre  in  Ashlar  Work. 

considerable  amount,  the  centre  must  be  strong  enough  to 
support  them  without  risk.  This  design  of  arch,  which 
has  a  leaning  to  the  Moorish  or  horseshoe  pattern,  is  greater 
than  a  semicircle,  and  was  used  in  a  large  building  in 
Brooklyn,  N.  Y.,  some  time  since.  In  this  case  the  centre 
was  carried  on  the  projecting  imposts  of  the  capitals. 

The  centres  of  Gothic  arches  are  many  and  varied  in 
form;  but  they  are  easily  struck,  however,  from  the  central 
point  or  radii  shown  by  architects  in  their  detail  drawings. 


28 


PRACTICAL   CENTRING. 


The  simplest  to  strike  out  is  the  equilateral  arch  centre, 
shown  in  Fig.  29.     The  centres  for  striking  the  curves  are 


SPRING  LINE 

FIG.  29.  —  Equilateral  Arch. 


plainly  indicated.  The  head  or  rise  of  the  arch  is  equal  to 
the  span  or  width.  From,  this  it  will  be  seen  that  straight 
lines  joining  the  apex  with  the  base  will  form  an  equilateral 


FIG.  30. — Laying  out  the  Bearers  for  a  Gothic  Arch. 

triangle.     The  centres  for  striking  out  the  curves  for  bear- 
ers, therefore,  will  be  on  the  base  or  spring  line,  as  A  and  B. 


FIG.  31.— Plan  of  Centre. 

B  C  in  Fig.  30  is  a  rod  striking  the  left  curve.     From  A  to 
the  apex  D  all  stone  or  brick  joints  run  in  the  direction  of 


PRACTICAL   CENTRING. 


C  B.     Fig.  3 1  is  a  plan  of  the  centre  without  the  apex  ties, 
showing  the  edges  of  the  bearers  and  lower  tie-pieces. 
The  obtuse  point  or  drop  arch  illustrated  in  Fig.  32  is 


CENTER  SPRING     LINE 

FIG.  32. — Centre  for  a  Drop  Arch. 


constructed  from  centres  on  the  base  line.  The  radius  is 
less  than  the  span.  It  will  be  easily  understood  from  the 
preceding  description.  All  braces,  however,  must,  as  is 
shown,  run  in  the  direction  of  the  centres,  from  which  the 


^CENTER  CENTE 

FIG.  33. — Another  form  of  Drop  Arch. 

curves  are  struck.  This  arch  is  supposed  to  be  6  ft.  in 
span.  Fig.  33  illustrates  another  arch  of  the  same  charac- 
ter, the  radii  of  which  run  to  centres  far  below  the  spring 


30  PRACTICAL    CENTRING. 

line,  being  on  the  jamb  line  and  drawn  square  to  the  spring 
line.  The  lancet  Gothic  arch,  Fig.  34,  has  striking  cen- 
tres, which  are  likewise  on  the  spring  line,  but  differs  from 
those  described  last  in  the  radius  being  longer  than  the 
width  of  the  span.  The  lines  join  in  a  way  to  form  an 
isosceles  triangle,  the  height  of  which  is  greater  than  the 
width.  For  large  centres,  calling  for  long  bearers,  the 
method  followed  in  the  sketch  is  the  best,  having,  if  such 


RADIUS 
OF  BEAREPS 


,Q   FEET — -*^ 

FIG.  34. — Lancet  Gothic  Arch. 

is  needed,  the  extra  brace  shown  by  the  dotted  lines.  This 
should  be  inserted  and  nailed  to  the  joint  tie-piece.  Small 
centre  bearers,  of  course,  can  be  cut  out  of  one  piece  of 
board,  as  already  described.  Joints,  lines  and  braces  must 
run  on  radial  lines. 

Tudor  arches  vary  much  in  shape,  and  are  all  struck 
from  centres  within  the  arch.  The  arch  represented  at 
Fig.  35  is  struck  from  four  centres,  two  of  which  are  on  the 
spring  line,  and  formed  by  dividing  the  spring  line  into 


PRACTICAL   CENTRING. 


CENTER  CENTER 

FIG.  35.— Centers  for  a  Four  Centre  Arch. 


CENTER  2  t. - 


CENTER  3 


FIG.  36.— Diagram  of  a  Three  Centre  Arch. 


32  PRACTICAL   CENTRING. 

four  equal  parts,  the  two  outside  divisions  indicating  the 
radii  required  for  the  lower  curves.  The  centres  for  the 
upper  curves  are  found  by  taking1  the  whole  width  of  the 
span  as  radius  and  cutting  the  line  of  the  jamb  with  this, 
radius,  as  shown  in  Fig.  35.  The  intersection  will  be  the 
centre  desired,  and  the  radius  will  be  to  the  tangential 
point  of  the  small  curve.  However,  as  centres  are  usually 
given  by  the  architects  to  strike  out  all  arches,  the  above 
will  be  sufficient  to  aid  the  beginner  when  he  meets  this 
arch.  It  will  be  noticed  that  as  the  joint  of  the  curve 
bearers  is  above  the  tangential  point,  so  all  braces  must  run 
to  the  centres  for  the  upper  curves.  Fig.  36  is  a  three- 
centre  arch,  showing  one  bearer,  the  striking-out  points,, 
and  radii. 


CHAPTER  V. 

CENTRING    CIRCULAR    WINDOWS. 

frequent  occurrence  of  circular  windows  in  the 
fagades  of  ecclesiastical  edifices  often  causes  contrac- 
tors some  difficulty  in  erecting  temporary  centres  to  sustain 
the  voussoirs  above  the  spring  line  until  the  bond  is  com- 
plete. A  comparatively  simple  method  is  shown  in  the 
illustration,  based  on  the  chordal  system,  and  consists  of  the 
usual  centre  proper  and  its  supporting  auxiliaries.  The 
peripheral  truss  of  the  centre  is  constructed  on  the  old  prin- 
ciple of  pieces  sawed  to  the  sweep  abutting  together  in 
joints  whose  planes  are  in  the  direction  of  the  radii  of  the 
centre  of  the  circle,  the  joints  being  secured  by  similar 
pieces  across  the  back,  breaking  joint.  This  construction  is 
held  together  by  a  tie-piece,  the  bottom  edge  of  which  is 
supported  at  the  radial  joints  by  struts  directed  from  the 
centre  of  the  circle,  the  whole  being  firmly  nailed  together. 
Two  of  these  frames  are  employed,  placed  equidistant  from 
each  other,  equal  to  the  thickness  of  the  stone  facing.  On 
the  edges  of  the  periphery  the  battens  or  pieces  which  form 
a  smooth  surface  on  which  to  lay  the  voussoirs  are  affixed, 
and  two  cleats,  as  shown,  are  fastened  across  the  lower 
edges  of  the  tie-pieces.  This  operation  gives  a  strong,  safe 
centre  for  arches  up  to  15  ft.  in  diameter.  The  dimensions 
of  the  pieces  are  as  follows :  Pieces  on  periphery,  i  y2  X 
8  in.;  tie-pieces,  1^X8  in.;  struts,  1^X3  in.;  battens,. 
1^X2  in.  The  supports  are  few  in  number  and  cut  in 
as  represented.  The  bottom  piece  (in  compression)  is 
placed  level,  bearing  on  the  intrados  at  the  points  A  and 
B.  From  these  points  pieces  reach  to  the  cleats,  C  and  D, 
and  at  the  spring  line  hold  the  centre  proper  in  its  posi- 
3 


34 


PRACTICAL    CENTRING. 


tion.  From  the  point  A,  also  resting  on  the  joint  A,  the 
tie-piece  A  E,  parallel  to  B  D,  supports  the  centre  of  the 
tie-piece  which  receives  the  thrusts  of  the  braces  above. 
Similarly  B  F,  parallel  to  A  C,  sustains  a  like  strain,  both 


FIG.  37. — Centring  for  Circular  Window. 

pieces  abutting  against  the  bolster,  E  F.  The  vertical 
piece  shown  can  be  inserted  if  it  be  necessary  for  additional 
security,  and  the  sustaining  pieces  can  either  be  of  two  sets 
— that  is,  one  under  each  separate  truss — or  if  the  wall  be 
-only  a  facing  of  moderate  thickness,  one  will  be  sufficient. 


CHAPTER  VI. 


SUSPENDED      CENTRES 


following  existing  method  of  forming  temporary 
'  supports  and  centres  in  the  construction  of  fire-proof 
floors   may  prove   useful.      The   first   example,    Fig.    38, 
shows  a  terra-cotta   floor,  after   being  laid  between  two 


FIG.  38. — Terra-Cotta  Arching  on  Suspended  Planking. 

Yearns.  As  will  be  noticed,  it  rests  on  a  staging  of  il/i  in. 
mason's  plank,  resting  on  a  4X4  in.  joist, which  is  supported 
by  a  y%  in.  iron  hook,  which  has  on  the  upper  end  a  screw 
thread  and  nut.  This  hook  is  made  like  Fig.  39.  The 


FIG.  39. — Hanger  for  Carrying  Suspended  Joist. 

hook  passes  through  the  \y2  in.  plank  and  through  another 
4  X4  in.  joist, which  rests  across  the  top  side  of  the  beam,  and 
is  bored  out  to  allow  it  to  pass  through,  from  which  the 


30  PRACTICAL   CENTRING. 

staging  is  suspended  and  held  securely  by  the  nuts  and 
washers.  Three  or  more  of  those  are  used  as  is  necessary, 
according  to  the  size  of  the  floor.  The  utility  of  this 


FIG.  40. —Centre  for  Small  Arches. 

method  is  apparent,  as  it  leaves  the  floor  or  space  under- 
neath perfectly  free  from  incumbrance,  and  the  temporary 
staging  can  be  more  safely  lowered,  thereby  providing 
against  accidents  in  case  the  terra-cotta  should  not  be  suf- 
ficiently bonded  and  drop  down.  The  hooks  used  generally 
are  of  ^  or  ^  in,  round  iron,  long  enough  to  suit  the 
depth  of  the  beams,  plus  the  thickness  of  the  joints,  and  a 


FIG.  41. — Arch  Turned  on  Suspended  Centres. 

brick  is  generally  left  out  where  the  hook  passes  through. 

Fig.  40  represents  the  way  in  which  masons  temporarily 

support  their  arched  brick  floors ;  in  this  case  an  arch  of 

small  space.     The  drawing  shows  the  ordinary  form  of  tim- 


PRACTICAL    CENTRING. 


37 


"her  centre  hung  from  a  joist  across  the  top  side  of  the 
"beam  by  bolts,  which  pass  through  another  joist  on  the 
bottom  side  of  the  centre  which  rests  on  it.  These  centres 
are  generally  made  from  five  to  eight  feet  in  length,  ac- 
cording to  convenience,  and  are  moved  along  as  section 
after  section  is  completed.  They  can  be  lowered  in  a  sim- 
ilar manner  to  Fig.  38,  with  the  nuts  on  the  top  edges  of 
the  upper  joists. 

In  Fig.  41  the  projection  of  a  brick  arch  turned  on  its 


FIG.  42. — Bottom  View  of  Centre,  Showing  its  Position  between  Girders. 

necessary  centre  is  seen  with  suspending  joist  and  the  low- 
ering nuts.  The  centre  differs  from  the  others  in  not 
liaving  any  bottom  joist,  but  merely  a  bottom  2  in.  strip, 
tying  the  frame  together,  through  which  the  bolts  pass, 
each  bolt  being  close  to  each  frame,  as  in  Fig.  42.  The 
frames  in  these  centres  are  spaced  comparatively  close  to- 
gether, to  support  the  dead  weight  above  them  when  laying 
the  brick. 


CHAPTER  VII. 

OBLIQUE     OR     SKEW     CENTRES. 

IN  order  to  make  a  skew  centre  it  will  be  necessary  to 
first  explain  to  the  reader  what  a  skew  arch  really  is. 
Mr.  Peter  Nicholson,  in  his  "  Encyclopedia  of  Architecture," 
defines  it  as  "  an  arch  the  face  of  which  stands  obliquely 
with  reference  to  the  inner  faces  of  the  piers/'  He  likewise 
states  that  "  the  first  skew  arch  was  built  across  the  Mugone 
River,  at  Florence,  Italy,  A.  D.  1550." 

From  Mr.  E.  Dobson's  useful  little  book,  "The  Art  of 
Building,"  we  take  the  following:  "The  skew  arch  is  one 
in  which  it  is  not  possible  to  lay  the  courses  parallel  to  the 
abutments;  for  were  this  done,  the  thrust  being  at  right 
angles  to  the  direction  of  the  courses,  a  great  portion  of 
the  arch  on  each  side  would  have  nothing  to  keep  it  from 
falling.  In  order  to  bring  the  thrust  into  the  right  direc- 
tion, the  courses  must  therefore  be  laid  as  nearly  as  possible 
at  right  angles  to  the  fronts  of  the  arch  and  at  an  angle  with 
the  abutments,  and  it  is  this  which  produces  the  skew  or 
oblique  arch." 

The  statics  or  construction  of  the  masonry  of  the  arch 
proper  is,  however,  slightly  apart  from  this  book,  which 
is  written  to  explain  to  carpenters  the  proper  method  to 
follow  in  building  the  centre  necessary  to  turn  the  arch. 
We  think  our  readers  will  find  it  instructive  and  useful  in 
practice.  Fig.  43  represents  the  constructed  centre  look- 
ing down  from  above,  and  shows  it  complete  and  ready  for 
setting  in  position,  a  a,  b  b,  c  c  and  d  d  being  the  main 
frames,  constructed  in  the  manner  shown  at  A,  Fig.  44, 
which  is  simple  in  form  and  still  strong  and  fit.  As  the 
arch  penetrates  the  wall  at  an  angle  of  45  degrees,  it  fol- 


PRACTICAL   CENTRING.  39 

lows  that  the  shape  of  the  front  elevation  or  face  will  be  a 
regular  ellipse,  as  shown  in  outline  over  e  F,  Fig-.  44. 
This  curve  is  found  by  dividing  the  circumference  of  the 
semicircular  frame,  e  e  e,  into  any  number  of  equal  divisions, 
then  transferring  these  divisions  by  ordinates  drawn  per- 
pendicular to  the  spring  line,  cutting  the  diagonal  seat  of 
the  elliptic  elevation  e  F,  Fig.  44.  From  these  points,  by 
raising  up  perpendiculars  to  e  F  and  making  them  equal  in 
height  to  those  at  e  e  e,  points  will  then  be  found  through 
which  the  exact  curve  of  the  elevation  can  be  traced.  A 
frame  must  be  made  to  this  curve,  and  have  its  edge  bev- 
elled to  the  angle  of  45  degrees  on  the  plan,  as  shown  on 


FIG.  43. 

the  right  side  at  Fig.  45,  so  that  the  battens  will  fit  close 
to  arris  formed  by  the  face  and  top  edge  of  the  frame,  which 
will  be  placed  as  e  F,  Figs.  43  and  44.  There  will  also  be 
two  half  frames  or  bearers  required  like  Fig.  46,  one  at 
each  end,  which  are  to  have  their  upper  ends  sawn  to  a 
mitre  or  angle  of  45  degrees,  to  fit  against  the  inside  face 
of  the  elevation  frame,  e  F,  and  be  securely  nailed  to  it 
square  with  the  sides  e  F.  To  put  this  centre  together,  lay 
the  longitudinal  stringer  bearers,  P  P,  Fig.  45,  down  on 
the  floor  and  tack  on  each  frame  in  its  position,  as  shown 
by  the  dotted  lines  at  Fig.  43,  and  then  after  bracing  the 
whole  construction  square,  by  squaring  the  bearers,  e  F, 
Fig.  43,  with  the  frames,  a  a,  bb,  c  c,  dd,  nail  the  battens 


4o 


PRACTICAL    CENTRING. 


II 


iSSSimlliMP^* 


FIG.  44. 


FIG.  45. 


PRACTICAL    CENTRING.  41 

round  till  they  are  all  on.  Afterwards  saw  off  the  project- 
ing ends  flush  with  the  faces  of  the  front  frames.  The 
skew  centre  must  now  be  turned  up  and  the  stringer  bearers 
nailed  on  solid,  and  the  centre  is  ready  for  setting.  Great 
care  must  be  exercised  in  setting  this  form  of  centre  in  or- 


FIG.  46. 

der  that  it  may  be  perfectly  level  at  the  spring  line  and 
across  on  the  stringer  bearers.  It  should  be  set  on  good 
uprights  resting  on  oak  wedges  of  slight  taper  and  be  well 
braced,  to  be  conveniently  eased,  immovable  and  not  likely 
to  be  jarred  out  of  its  proper  position.  This  is  important 
to  a  good  result. 


CHAPTER  VIII. 

FLARING  OR  SPLAYED  CENTRES. 

THE  essential  appliances,  termed  centres,  though  usually 
of  a  simple  character,  ofttimes  assume  uncommon 
forms,  and  in  this  chapter  we  place  before  our  readers 
something  which  the  majority  are  likely  to  be  unfamiliar 
with.  They  occur  generally  in  the  construction  of  ecclesi- 
astical or  public  buildings,  and,  as  the  art  of  building  fre- 
quently forces  carpenters  and  builders  to  use  knowledge 
outside  of  routine  practice,  it  will  be  wise  for  our  readers 
to  be  familiar  with  their  construction  in  case  they  require 
it.  Building  is  a  progressive  art,  and  we  can  say  from  ex- 
perience that  it  is  always  best  to  keep  ahead  in  the  matter 
of  information,  in  order  that  there  may  be  no  possibility 
of  ever  being  retarded  by  a  difficulty. 

Flaring  or  splayed  centres  are  those  that  open  or  spread 
outward,  and  are  used  to  form  or  turn  splayed  arches  whose 
soffits  also  flare  or  widen  to  the  front.  These  are  the  out- 
come of  the  use  of  very  thick  walls,  and  were  largely  intro- 
duced by  the  mediaeval  builders  for  the  purpose  of  spread- 
ing the  light  to  either  side,  which  would  be  impossible 
were  the  splayed  sides  omitted ;  also  for  lessening  the  ap- 
parent great  thickness  of  the  walls.  When  the  jambs  were 
thus  moulded  it  necessarily  followed  that  the  soffit  of  the 
arch  should  be  similarly  treated,  and  it  is  to  explain  how 
the  centres  for  turning  them  were  constructed  that  this 
article  was  written.  That  the  mediaeval  builders  employed 
them  cannot  for  a  moment  be  doubted,  and  it  is  not  meet 
that  we  of  the  nineteenth  century  should  be  deficient  in 
any  knowledge  which  our  predecessors  wielded  to  so  much 
advantage. 


PRACTICAL   CENTRING. 


43 


Reference  to  Fig.  47  of  the  illustrations  shows  a  centre 
for  a  splayed  semicircular  arch  of  4  ft.  span,  with  a  splay  of 


FIG.  47. 

8  in.  in  12  in.  depth  of  jamb,  which  will  be  seen  by  measuring 
the  side  view  of  the  completed  centre  drawn  to  the  right. 
This  centre,  like  all  the  others  previously  described,  will 


FIG.  48. 

require  two  frames,  as  A  and  B,  Figs.  47  and  48,  each  of 
which  will  be  of  a  different  diameter  and  struck  from 
a  different  radii;  that  is,  the  smaller  frame  will  have 


FIG.  49. 

its  edge  made  to  a  curve  struck  with  a  i  ft.  1 1  in. 
radius,  and  with  the  larger  struck  with  a  2  ft.  7  in.  radius. 
The  edges  of  these  frames  must  be  bevelled  all  round  to 


44 


PRACTICAL   CENTRING. 


the  splay  shown  on  the  side  view,  in  order  that  the  battens 
will  fit  closely  to  them  and  make  the  necessary  angle  to 


FIG.  50. 

which  the  arch  will  be  turned.  ,  The  reader  will  understand 
this  better  by  looking  at  the  right  side  of  the  sketch  (Fig. 


PRACTICAL    CENTRING. 


45 


47)  at  the  elevation  of  the  frames  where  the  bevelled  edges 
are  shown,  only  one-half  of  them,  being  covered  with  bat- 
tens. The  plan  of  the  centre,  Fig.  48,  also  shows  this 
more  distinctly,  and  also  the  bevels  of  the  frames  wrought 
to  the  angle  of  the  splay.  Carpenters  will  require  to  exer- 
cise a  little  more  care  in  constructing  this  form  of  centre 
than  is  usually  done,  as  it  is  for  a  special  purpose.  Fig.  49 
is  the  elevation  of  the  large  frame,  and  is  slightly  different 
in  construction  from  the  smaller.  Fig.  50  is  the  elevation 
of  a  Gothic  window  having  jambs  and  soffit  with  a  double 
flare  or  splay,  which  is  done  to  break  the  excessive  depth 


FIG.  51. 

of  surface  consequent  on  a  thick  wall.  As  the  plan  shows , 
two  centres,  which  flare  at  different  angles,  will  be  needed 
here,  or  one  centre  with  two  flares  of  unequal  angles.  The 
first  method  is  the  best,  however;  that  is,  to  make  two 
separate  centres  and  bolt  them  together  so  they  will  fit  at 
the  spring  line,  A  B,  in  the  manner  necessary  to  enable  the 
mason  to  properly  turn  his  arch.  There  is  very  little  dif- 
ference between  this  appliance  and  the  one  described  above, 
that  is,  taking  each  centre  singly,  but  as  there  is  a  double 
splay,  then  there  must  be  a  double  centre  in  order  to  turn 
the  arch.  One  may  be  seen  by  referring  to  Fig.  5 1  of  the 
illustrations,  and  the  reader  will  have  no  difficulty,  from 


PRACTICAL   CENTRING. 


PRACTICAL   CENTRING.  47 

-what  has  already  been  said,  in  making  a  centre  of  this 
kind. 

In  connection  with  this  subject  our  readers  will  doubtless 
meet  some  very  unique  modes  of  applying-  it.  One  which 
has  come  to  my  notice  is  that  which  Mr.  James  Renwick, 
the  senior  member  of  the  firm  of  Renwick,  Aspinwall  & 
Russell,  of  New  York,  introduced  into  the  new  Church  of 
All  Saints,  at  i29th  Street  and  Madison  Avenue,  New  York 
City.  Here  it  is  placed  in  many  ways,  as  at  Figs.  50  and  5  i ; 
also  in  a  window-opening  embracing  twin  Gothic  windows 
which  had  splayed  jambs,  as  A  B,  Fig.  50,  and  on  the  in- 
side wall  they  were  spanned  by  a  four-centre  arch  forming 
a  recess  of  another  flare,  as  B  C,  Fig.  50,  which  made  up  the 
full  thickness  of  the  wall.  Another  way  in  which  it  was 
used  was  that  represented  at  Fig.  52.  '  This  form  of  centre 
was  employed  in  turning  the  arches  of  the  arcades  dividing 
the  nave  and  right  and  left  aisles.  It  was  adopted  because 
the  soffits  of  the  arches  were  built  V-shaped  in  order  that 
plaster  mouldings  might  be  readily  run  on  them.  The 
whole  construction  was  as  described  before,  and  made  up  of 
two  centres  of  the  same  splay,  which  were  bolted  together 
in  the  manner  shown  in  the  side  view  drawn  in  the  centre 
of  Fig.  52,  where,  to  the  left,  is  shown  the  battens  covering 
the  frames,  and,  to  the  right,  the  exposed  frames  before 
the  battens  are  nailed  on.  On  account  of  the  large  sweep 
of  the  curves  of  the  arch  (which  was  about  1 5  ft.  span)  and 
the  necessity  for  economizing  material  and  labor,  the  car- 
penter was  compelled  to  use  sound  judgment  in  framing 
his  centre,  that  it  might  be  sufficiently  strong  to  sustain  the 
superincumbent  weight ;  so  a  trussing  system  was  followed 
in  constructing  it. 


CHAPTER  IX. 

TWO    EXAMPLES    OF    CENTRES    SUITABLE    FOR    WIDE    SPANS. 

AS  the  centring  of  arches  is  a  detail  of  builders'  practice 
which  is  continually  involving  special  forms  of  con- 
structive carpentry  to  sustain  the  superincumbent  weight 
placed  on  the  centre,  I  deem  it  advisable  to  place  before 
the  reader  two  principles  of  construction  which  are  excel- 
lent. The  first,  Fig.  53,  was  used  in  the  new  office  build- 


FIG.  53. — Centre  for  Semi-circular  Arch  of  20  ft.  Span. 

ing  recently  erected  by  Messrs.  Jackson  &  Co.,  of  Union 
Square,  in  New  York.     As  will  be  noticed,  it  was  entirely 


PRACTICAL    CENTRING. 


49 


constructed  without  bolts  or 
any  ironwork  of  any  kind 
excepting  the  nails  necessary 
to  hold  the  framed  joints 
together.  The  trussing  was 
most  economically  done,  and 
the  timbers  kept  uninjured. 
At  the  same  time  the  heavy 
stone  forming  the  ring  of  the 
arch  were  ably  carried.  This 
centre  was  20  ft.  span  and 
carried  a  24  in.  wall.  The 
centre  for  the  segmental  arch, 
illustrated  at  Fig.  54,  is  a 
trussed  form,  which  might  be 
followed  with  safety;  but  a 
still  better  method  would  be 
to  carry  the  feet  of  the  braces 
over  to  the  suspension  rods 
on  the  chord.  In  concluding 
this  interesting  subject  I 
would  recommend  those  who 
have  occasion  to  use  centres 
to  always  be  on  the  safe  side 
and  make  their  construction 
more  than  strong  enough,  for 
there  are  very  many  cases  re- 
corded in  the  history  of  build- 
ing construction  where  insuf- 
ficient or  improper  centring 
has  caused  the  failure  of  valu- 
able works. 
4 


CHAPTER  X. 

SEWER      CENTRES. 

THE  centres  previously  described  are  those  mostly  used 
in^  the  construction  of  buildings,  but  these  appliances 
are  also  requisite  in  the  construction  of  subterranean  struc- 
tures, such  as  sewers.  It  is  for  the  purpose  of  showing  the 
carpenter  how  to  make  them  correctly  that  this  form  of 
centre  is  now  described.  Ordinary  brick  sewers  are  gene- 
rally built  in  two  ways — of  cylindrical  and  of  egg-shaped 
sections ;  that  is,  in  the  ordinary  sewers  used  in  general  street 
work  throughout  the  country.  As  the  section  of  a  sewer  cut 
through  at  right  angles  is  comparatively  familiar  to  all  car- 
penters, it  would  seem  almost  unnecessary  to  reproduce  it 
here;  still  the  writer  thinks  it  safer  to  show  how  the 
centre  used  in  turning  the  arch  is  made  and  set. 

Fig.  55  of  the  illustrations  represents  the  cross  section 
(cut  at  right  angles  to  the  direction  of  its  length)  of  a 
circular  or  cylindrical  sewer  whose  diameter  or  bore  is  2 
ft.,  with  the  lower  part  or  invert  and  the  upper  part  or  arcli 
turned  on  the  centre  required.  To  build  the  invert  to  the 
shape  shown,  the  mason  works  and  guides  the  construction 
by  moulds  or  templates  put  together  after  the  manner  of  the 
frames  described  before, using  two,  and  stretching  lines  from 
one  to  the  other  to  guide  the  courses  of  brickwork  as  he 
goes  along.  He  usually  builds  a  sewer  in  lengths  or  sec- 
tions of  six,  eight  or  ten  feet  at  a  time.  When  the  lower 
course  is  built  up  to  a  height  of  one  course  of  brick  above 
the  spring  line,  as  shown  in  the  illustration.  Fig.  55,  the 
centre  is  set  in  the  manner  as  drawn  here,  resting  on  three 
pieces  of  2X4  in.  stud  stuff  placed  under  each  end  of  the 
centre  proper.  This  centre,  unlike  those  described  hereto- 


PRACTICAL    CENTRING.  51 

fore,  is  made  in  a  long  length  measuring  6,  8  or  10  ft.,  so 
that  the  arch  covers  what  has  been  built  of  the  lower  part. 
It  will  be  noticed  that  the  centre  is  set  about  2  J^  in.  above  the 
spring  line,  which  is  done  so  it  may  be  handily  lowered  and 
slid  out,  thus  making  it  available  for  the  next  length  of 
sewer.  It  will  likewise  be  noticed  that  the  supporting 
uprights  are  all  loose,  so  that  they  may  be  readily  knocked 
away  to  permit  the  centre  to  drop  down  to  the  spring  line 
or  widest  part  of  the  cylindrical  bore,  and  by  this  means 
loosening  it  and  allowing  it  to  slide  freely  out.  Readers 


FIG.  55. 

will  readily  comprehend  that  it  would  be  impossible  to  ease 
the  centre  were  it  set  at  the  spring  line  in  the  manner  of 
wall  centres. 

Carrying  the  subject  further  along,  the  egg-shaped  form 
is  shown  at  Fig.  56,  where  the  constructed  sewer  is  drawn 
in  isometrical  projection,  part  of  the  brickwork  being  left 
off  to  give  the  reader  a  clearer  idea  as  to  how  the  centre 
is  placed  above  the  spring  line.  The  bottom  portion  is,  as  in 
the  case  of  the  last,  built  from  a  template  which  is  made  by 
the  carpenter.  In  order  to  make  this  template  to  the 
proper  shape,  it  must  be  laid  out  by  a  geometrical  process 


52  PRACTICAL    CENTRING. 

to  the  outline  shown  on  the  engineer's  drawings,  so  it 
would  be  well  for  the  reader  to  thoroughly  understand  how 
this  is  done.  Fig.  57  explains  the  method  by  which  egg- 
shapes  are  laid  down.  A  B  is  a  centre  line  or  plumb  line, 
and  C  D  any  other  line  drawn  at  right  angles  to  it.  With 


FIG.  56. 

the  intersection  of  the  lines  as  centre  and  12  in.  radius  strike 
the  semicircle  CAD.  Produce  C  D  to  E  F  and  make  C  E 
and  D  F  equal  to  C  G.  Now  make  G  B  equal  to  C  D,  and 
divide  B  G  into  four  equal  divisions.  Next  take  H  as 
centre  and  H  B  as  radius  and  describe  the  circle  shown. 


PRACTICAL    CENTRING. 


53 


From  E  and  F  as  centres,  with  E  D  and  F  C  as  radii,  strike 
arcs,  joining  the  smaller  bottom  circle  with  the  larger,  C  A 
D,  which  will  complete  the  figure.  The  template  to  be 


*.— — 4°- * 


FIG.  57. 

made  to  the  outline  C  B  D  is  represented  at  Fig.  58,  where 
the  method  of  putting  it  together  is  exemplified.  This  fig- 
ure should  be  laid  out  on  a  drawing  board  or  floor,  and  the 


FIG.  58. 

two  side  pieces  marked  and  sawn  to  the  outline  of  the  bot- 
tom portion  of  the  egg-shape.     The  centre  necessary  for 


54 


PRACTICAL    CENTRING. 


the  arch  is  made  as  described  above,  and  for  a  sewer  of 
these  dimensions  might  have  the  parts  of  the  following- 
sizes:  Stuff  to  be  rough  spruce  or  pine  strongly  nailed 
together;  frames  i  j£  in.  thick,  battens  i  in.  or  i^in.  thick, 
supporting  uprights  2x4  in.  In  connection  with  this  sub- 
ject of  sewer  centres  a  very  peculiar  feature  is  shown  at  Fig. 
59.  It  is  the  plan  or  top  view  of  a  centre  forming  the  con- 
tinuation of  the  arch  from  one  street  to  another,  or,  prop- 


FIG.  59. 

erly,  a  rectangled  bend  in  the  sewer.  In  building  this  the 
carpenter  will  make  the  frames  or  bearers  radiate  to  a  com- 
mon centre,  as  Fig.  59,  and  be  obliged  to  cut  the  battens 
to  a  curve  the  shape  of  which  can  be  determined  by  the 
following  process:  Let  A  B  C  D,  Fig.  60,  be  the  plan  of 
the  annular  or  ring  vault  to  be  turned.  It  is  required  to 
find  the  shape  of  the  covering  boards  or  battens  which  will 
be  nailed  on  the  frames.  The  edges  of  the  frames  being 


PRACTICAL   CENTRING. 


55 


56  PRACTICAL    CENTRING. 

-wrought  to  the  semicircular  curve,  A  E  B,  we  proceed  to 
lay  out  the  boards.  Divide  the  quarter  circle  or  quadrant 
into  nine  equal  parts,  as  B  H,  H  I,  I  J,  J  K,  K  L,  L  M,  M  N, 
N  O  and  O  E.  Join  these  points  of  division  by  lines,  and 
produce  them  till  they  meet  the  line  G  C.  Now  with  R  as 
centre  and  J  as  radius  strike  the  arc  shown,  also  with  R  as 
centre  and  K  as  radius  strike  another  arc.  With  S  as  cen- 
tre and  S  K  as  radius  strike  ah  arc,  also  with  I  as  centre 
strike  another.  Next  take  T  as  centre,  and  continue  in  this 
way  until  there  is  a  board  for  each  division  in  the  semi- 
circle. These  boards  can  be  cut  in  short  lengths  and 
joined  on  the  several  frames  by  butt  joints,  but  these  butt 
joints  must  be  on  the  radius  lines.  On  account  of  the  diffi- 
culty of  removing  a  small  centre  of  this  kind,  I  would  sug- 
gest that  builders,  if  they  desire  to  use  the  centre  on 
another  corner,  have  only  a  short  section  made,  as  A  B  C  D, 
Fig.  59.  By  this  means  they  can  build  the  entire  curved 
arch  in  short  sections,  and  move  the  centre  for  each  as 
required;  but  where  it  is  possible,  the  best  way  is  to  con- 
struct the  whole  centre,  and  knock  it  to  pieces  when  the 
arch  is  turned  and  the  mortar  set. 

In  regard  to  building  manholes,  which  are  necessary  on 
all  street  sewers,  there  seems  to  be  one  way  which  almost 
all  masons  follow;  that  is,  to  use  guide  lines  stretched  from 
templates  in  the  manner  represented  in  the  drawing, 
Fig.  61.  Sewers  are  fitted  with  chambers  placed  at  con- 
venient distances  for  the  purpose  of  cleaning  and  examina- 
tion, and  they  are  connected  with  the  street  level  by  a  brick 
manhole,  so  that  they  can  be  entered  by  men  and  worked  at. 
They  are  generally  built  in  the  shape  shown  in  Fig.  6 1 ,  or 
to  a  section  of  truncated  cone,  this  being  considered  the 
strongest  form  for  the  purpose,  and  the  brick  structure  is 
topped  or  covered  with  a  cast-iron  cap  and  removable  cover 
set  flush  with  the  street  level.  To  make  the  templates  or 
moulds  required  is  a  very  simple  operation,  though  it  in- 
volves the  principle  before  described,  and  consists  in  making 
two  disks  or  rings  of  the  diameter  called  for  in  the  engineer's 
plans  and  specifications,  one  for  the  bottom  and  one  for  the 


PRACTICAL    CENTRING. 


57 


FIG.  61. 

top.  The  top  template  is  supported  at  the  necessary  height 
and  set  level,  and  the  bottom  template  is  placed  on  the  cir- 
cular opening  in  the  chamber  below,  and  the  lines  are  fas- 
tened to  the  edges  of  each  template  from  nails  driven  into 
them.  The  mason  or  bricklayer  carries  up  his  courses  of 
brick  level,  turning  them  round  these  lines  as  he  goes  up. 


CHAPTER  XI. 


HOW    TO    MAKE    A    DIMINISHING    PLUMB    RULE. 


.—Scale 


is  so  little  to  be  said  about  making^ 
plumb  rules — in  fact,  it  is  such  a  simple 
tool  for  any  ordinary  carpenter  to  make,  that  it 
seems  almost  superfluous  to  touch  on  the  sub- 
ject, still  I  think  there  is  one  which  is  more 
difficult  to  make  than  would  be  supposed,  and 
I  think  the  information  will  come  in  handy  to 
many  mechanics  and  builders.  The  plumb 
rule  which  carpenters  and  masons  usually  carry 
and  employ  is  only  applicable  when  the  work 
is  to  be  carried  up  perfectly  perpendicular  or 
plumb.  Consequently  the  two  edges  are  equi- 
distant or  parallel,  and  the  gauged  line  in  the 
centre  (over  which  is  stretched  the  plumb 
line  sustaining  the  bob  or  weight)  is  also 
parallel  to  both  edges,  and  when  it  is  applied 
against  the  work,  either  on  posts  or  brick 
walls,  the  line  must  swing  exactly  to  the  gauge 
line  before  the  work  can  be  called  exactly 
plumb.  There  are,  however,  structures  and 
details  of  construction  embraced  within  the  art 
of  building  which  are  not  built  perpendicular 
from  their  base  or  foundation,  but  for  various 
reasons  diminish  as  they  rise.  This  form  is 
generally  adopted  where  the  structure  is  car- 
ried up  to  a  great  height,  as  steeples,  spires, 
towers  and  factory  chimney  stacks,  for  the  pur- 
pose of  lessening  the  area  of  resistance  to  the 
wind,  increasing  the  area  of  the  base,  and  di- 


PRACTICAL   CENTRING. 


59 


minishing  to  the  top,  where  the  strain  is  greater  than  at 
the  base.  It  follows,  therefore,  that  the  mechanic  must 
contrive  the  diminishing  plumb  rule.  Supposing  A  to  be 
the  design  for  an  octagonal  factory  chimney,  which  is  to  be 


FIG.  63. 


FIG.  64. — How  to  make  a 
Diminishing  Plumb  Rule. 


s 


-L-+ 


n  4* 


..v 


FIG.  64.— One-half  Inch  Scale. 


erected  in  close  proximity  to  a  factory,  how  is  it  to  be 
started  and  carried  up  to  the  outline  drawn  by  the  architect 
and  what  is  the  arrangement  for  doing  it?  It  is  compara- 
tively simple  and  readily  comprehended.  The  first  thing 


•6O  PRACTICAL   CENTRING. 

to  be  done  is  to  very  carefully  take  all  the  measurements, 
which  must  not  be  done  to  scale,  but  will  be  figured  out  on 
the  details  by  the  architect.  This  stack  is  16  ft.  wide  at 
the  ground  line  and  diminishes  to  8  ft.  at  the  top,  below  the 
cornice  or  top.  Now,  the  carpenter's  duty  is  to  construct  a 
wooden  template  mould  or  pattern,  as  B,  exactly  to  the 
measurement  on  the  plans  for  the  outside  form,  and  a  semi 
or  full  circular  mould  for  the  base  or  shaft  inside,  so  that 
the  bricklayer  may  mark  this  shape  on  the  top  side  of  the 
foundation  and  lay  his  brick  neatly  to  it.  This  process  will 
give  the  octagonal  form  to  lay  the  first  course  by,  and  from 
this  the  other  courses  are  continued  one  on  top  of  another 
until  the  top  is  reached.  When  the  template  is  made  the 
plumb  rule  is  next  needed.  This  is  made  out  of  a  i  y±  in. 
clear  white  pine  board,  faced  up  out  of  wind,  gauged  to  1^ 
in.  thickness,  and  must  be  wide  enough  to  make  the  required 
rule.  One  edge  shall  be  jointed  perfectly  straight  by  using 
a  straight-edge  on  it,  and  shall  be  squared.  The  architect's 
detail  will  give  the  angle  of  diminution,  so  this  angle  must 
l>e  marked  off  from  the  bottom  squared  end  of  the  rule, 
which  may  be  any  convenient  width,  say  four  or  six 
inches,  or  wide  enough  to  permit  a  hole  to  be  made  for  the 
bob  to  swing,  and  rise  on  the  board  to  the  length  the 
mason  likes  best — four,  six  or  seven  feet.  When  this  is 
done  the  board  is  gauged  parallel  to  the  jointed  edge,  a 
liole  cut  for  the  bob  and  saw  kerf  made  to  hold  the  string 
at  the  top  end.  The  enlarged  sketch  C  shows  a  diminish- 
ing plumb  rule  placed  against  the  side  or  face  of  the  stack, 
with  its  left  side  diminishing  and  its  right  plumb.  This 
rule  is  7  ft.  long,  6  in.  wide  at  the  bottom,  and  8^  in.  at 
the  top,  or  the  diminution  is  2^  in.  in  7  ft.  The  entire 
•outline  of  the  whole  stack  depends  upon  the  plumb  rule 
and  the  way  it  is  used;  therefore,  I  cannot  insist  too 
strongly  on  its  being  made  extremely  accurate  and  to  the 
angle  laid  down.  It  is  a  very  good  plan  to  draw  the  line 
to  scale  the  length  or  height  of  the  intended  rule  and  space 
the  diminish  off,  or  the  architect  should  state  the  diminish 
as  i  in.  in  5  ft.,  2  in.  in  7  ft.,  and  so  on. 


PRACTICAL    CENTRING.  6 1 

Another  thing  often  requisite  in  a  rule  of  this  kind  is  to 
make  it  slightly  hollow  on  the  working  edge  so  as  to  curve 
the  outline  of  the  chimney  and  give  it  a  graceful  contour. 
In  concluding,  I  would  say  that  too  much  care  and  attention 
cannot  be  bestowed  on  special  tools  of  this  nature,  as  a  mis- 
calculation or  error  may  cause  very  serious  consequences.  . 


CHAPTER  XII. 

TRIMMING    WINDOWS    FOR    SHUTTERS. 

IT  should  be  the  care  of  every  builder  when  furring  out 
walls  by  studding,  for  the  boxing  for  shutters,  to  see 
that  they  are  kept  far  enough  back  from  the  line  of  the 
edge  of  the  casing  to  permit  the  back  linings  to  go  easily 
into  the  groove  of  the  casings.  Sometimes  a  great  deal  of 
time  is  lost  by  the  carpenter  being  obliged  to  hew  off  the 
studs,  in  order  to  get  the  back  linings  into  their  place, 
which  ought  never  to  occur.  It  is  much  better  to  have 
them  a  little  too  far  back  than  too  far  forward,  as  a  strip 
can  always  be  nailed  on  the  stud  to  fill  up  the  deficiency. 

When  no  elbows  and  shutters  are  used,  or  when  the 
panel-back  comes  flush  with  the  plaster  and  fair  with  the 
edges  of  the  jambs,  which  are  also  flush  with  the  plaster, 
the  panel-back  must  be  scribed  down  to  the  floor,  keeping 
the  stiles  plumb,  so  that  the  rail  will  sit  level,  and  the  top 
rail  fit  under  the  foot-bead,  which  is  rebated  out  to  receive 
its  thickness.  Before  nailing  in  position,  a  straight-edge  is 
placed  down  the  edges  of  the  jambs  resting  on  the  floor, 
and  the  floor  marked.  Measure  back  and  mark  the  thick- 
ness of  the  panel-back,  and  nail  a  strip  on  the  floor  to  pre- 
vent the  panel-back  from  driving  back  whilst  nailing. 
Next  place  it  in  its  place  under  the  foot-bead,  and  nail  it 
through  the  bead  into  the  top  edge,  and  toe-nail  the  bottom 
rail  into  the  floor. 

When  this  is  done  the  trim  can  be  put  on,  but  the  line 
of  the  face  of  the  jambs  must  be  marked  down  on  the  face 
of  the  panel-back,  so  that  the  base  blocks  and  casings  can 
be  nailed  on  the  same  line. 

In  front  windows  which  have  inside  shutters  a  longer 


PRACTICAL   CENTRING.  63 

operation  has  to  be  gone  through.  The  first  thing  done  is 
to  cut  out  the  dados  in  the  window  frame,  then  to  take  a 
rebate  plane,  shaving  off  the  tongues  of  the  soffit  and  back 
linings  together.  The  soffit  is  usually  ploughed  to  admit 
a  tongue  on  the  end  of  the  back  lining. 

When  nailed,  the  three  are  driven  tightly  into  the 
ploughing  on  the  frame  and  toe-nailed  into  the  casings, 
care  being  taken  to  see  they  are  not  too  wide  for  the  plas- 
ter. If  this  be  so,  then  the  soffit  must  be  made  narrower  by 
taking  the  same  stuff  off  both  edges,  so  that  the  rails  of  the 
soffit  may  show  of  equal  width  when  the  tongue  on  the 
inside  is  driven  into  the  groove  in  the  head  casing. 
Should  the  back  linings  be  panelled  they  must  be  reduced 
in  a  similar  way,  so  that  they  will  come  flush  with  the  plas- 
ter. The  elbows  are  then  nailed  to  the  panel-back  in  the 
grooves  which  are  prepared  for  them,  placed  in  the  window 
recess,  and  scribed  to  the  floor,  so  that  the  edge  of  top  rail 
will  come  exactly  to  the  bottom  of  the  groove  in  the  inside 
casing  nailed  on  the  sill,  in  order  that  the  ^  in.  thick  foot- 
bead  will  fit  into  the  groove  and  close  down  to  the  top  edge 
of  the  panel-back.  After  jointing  off  the  top  edges  of  the 
panel-back  and  elbows,  the  three  can  now  be  nailed  to  the 
floor  and  the  foot-bead  fitted  into  the  groove  on  top  of  the 
panel-back,  and  it  returns  into  the  grooves  on  the  back 
lining  on  the  top  edges  ot  the  elbows.  After  all  the  above 
has  been  completed  the  trim  can  be  nailed  on  as  before. 
When  shutters  are  used  the  groove  on  the  inside  casing  is 
generally  far  enough  back  from  the  face  of  the  jamb  to 
allow  space  for  the  combined  thickness  of  the  shutter  and 
back  folds  and  a  y2  in.  margin  outside  the  shutter,  and  the 
elbows  are  on  the  same  line  as  the  shutter,  so  that  the  foot- 
bead  breaks  the  joint. 

The  best  way  to  scribe  the  panel-back  or  panel-backs  and 
elbows  to  the  floor  is  as  follows : 

As  it  often  happens  that  the  frame  has  been  thrown  out 
of  square  by  the  settlement  of  the  building,  necessitating 
more  labor,  proceed,  after  jointing,  to  place  the  panel-back 
against  the  frame  in  the  recess,  and  plumb  one  stile  by 


64  PRACTICAL   CENTRING. 

furring  up  whichever  side  is  low.  Set  a  pair  of  compasses 
from  the  top  edge  of  the  casing  to  the  bottom  of  the  groove 
on  whichever  corner  of  the  frame  is  highest,  and  scribe  to 
the  floor.  After  scribing,  it  will  be  found  that  the  corner 
to  which  the  compasses  have  been  set  will  come  exactly 
right,  but  the  other  side  must  be  planed  off  until  it  comes- 
flush  with  the  under  side  of  the  groove. 

Another  suggestion  which  I  would  like  to  offer  is  this : 
To  furr  out  for  the  skirting  before  the  plaster  is  put  on, 
as  it  will  save  (when  it  is  on)  a  lot  of  time  digging  off  the 
plaster  for  the  furring.-  Again,  to  see  that  the  framers  get 
their  door  and  window  studs  exactly  plumb  both  ways.  It 
will  expedite  the  setting  of  the  door  jambs,  and  save  more 
plaster  cutting.  Builders  will  as  a  rule  generally  find  that 
a  little  care  in  setting  up  the  ground  work  will  save  much 
time  when  the  finish  is  being  put  on. 


CHAPTER  XIII. 

SETTING     JAMBS. 

ONE  of  the  most  important  and  too  often  neglected  things 
in  setting  jambs  is  to  block  behind  the  jambs  for  the 
screws  of  the  hinges.  In  rebated  jambs  this  blocking  is 
indispensable;  so  measure  down  about  6  in.  from  the  head 
and  9  in.  from  the  floor,  and  nail  in  a  4  in.  pine  block  on 
the  stud,  behind  the  jambs,  to  secure  the  screws.  Builders 
should  watch  sub-contractors  in  this  small  matter,  as  the 
screws  pull  out  when  they  have  no  thickness  to  hold  to. 

If  the  casing  have  a  beaded  or  moulded  edge  without 
corner  blocks,  the  top  corners  should  be  mitred  with  a 
mitre  jack  made  in  the  following  simple  manner: 

Take  a  piece  of  i  ^  in.  stuff,  and  i  in.  or  so  wider  than 
the  width  of  the  casing,  about  2  ft.  6  in.  long,  nail  a  fence 
or  piece  of  j£  in.  strip  on  both  edges,  rising  above  the  sur- 
face the  thickness  of  the  casing.  Now  take  a  bevel,  set  it 
exactly — not  nearly,  but  exactly — to  an  angle  of  forty-five 
degrees,  or  from  3  in.  to  5  in.  on  the  steel  square  (reverse 
the  bevel  to  see  if  the  angle  be  true) ,  and  mark  two  reverse 
mitres  across  the  edges  of  the  T/fa  in.  strips  and  the  surface 
of  the  bottom  or  wide  piece  and  over  one  edge — the  edge 
which  has  the  short  corners  of  the  bevels.  Saw  deep 
enough  into  the  wide  piece  on  this  marked  edge  to  cut 
through  the  bead  or  moulding  on  the  casing  when  it  is 
placed  between  the  fences  against  the  one  which  is  sawn 
into.  After  putting  the  casing  in  its  place,  'and  marking 
the  top  corner  with  a  knife,  the  casing  is  placed  against  the 
fence  with  the  mark  exactly  at  the  saw  cut,  and  having  the 
saw  outside  the  mark  so  as  to  slightly  leave  it  on  the  stuff. 
The  mitre  can  be  readily  and  instantly  sawn  without  using- 


66  PRACTICAL   CENTRING. 

a  bevel  or  a  template,  which  is  inaccurate  and  unmechani- 
cal.  The  bottom  end  must  fit  tightly  down  on  the  upper 
•end  of  the  case  block ;  if  not,  then  the  end  must  be  scribed 
to  the  block  with  the  compasses  before  mitring. 

All  casings  ought  to  be  level  across  the  face,  so  that 
when  a  straight-edge  is  placed  across  the  opening  it  will 
touch  all  their  surfaces.  The  head  should  also  be 
straight  with  the  stiles,  and  all  the  mitres  and  joints 
tightened  and  well  nailed.  All  mouldings  and  back  bands 
can  be  mitred  and  nailed  on  when  the  above  is  done,  and 
•the  mitres  will  come  tight. 

In  setting  back  window  jambs,  or  on  those  window 
frames  which  have  outside  blinds  with  a  panel-back  below 
the  sill,  the  following  is  the  best  way  to  proceed . 

First,  cut  with  a  chisel  on  a  straight  line  the  groove 
(where  it  stops  against  the  sides)  out  of  the  frame  casing, 
both  top  and  bottom,  on  both  right  and  left  casing,  and 
clean  all  the  mortar  and  dirt  out  of  the  ploughing.  Now 
take  the  short  rebated  jamb  for  the  head,  and,  getting  upon 
a  high  horse,  place  it  with  its  rebated  tongue  on  the  head 
groove,  and  mark  exactly,  with  a  sharp  knife,  the  inside 
corner  on  the  left  and  right-hand  groove.  Square  these 
marks  over  the  face  and  lay  out  a  dado  3/£  in.  wide  toward 
each  end.  Dado  this  laying  out  3/£  in.  deep.  Next  take 
the  right  and  left  jamb  and  square  one  end  of  each  in  pairs. 
Lay  out  a  tongue  3/£  in.  wide  from  these  square  ends  and 
y%  in.  thick,  gauged  from  the  faces.  Cut  these  tongues  out 
and  run  a  rebate-plane  shaving  off  the  back  side  of  the 
tongues  of  the  head  jamb  and  sides,  and  take  an  arris  of 
the  face  side.  This  will  let  the  tongue  go  easily  into  the 
grooves  in  the  frame.  Next  nail  the  head  on  the  sides, 
keeping  the  front  edges  flush,  and  break  off  the  over  length 
of  tongue  on  the  head  piece.  Set  the  tongues  of  the  jambs 
in  the  frame  grooves,  and  drive  the  jambs  in  till  they 
sound  solid.  Use  a  block,  so  as  not  to  bruise  the  edge 
when  driving.  When  they  are  in  solid,  mark  the  groove 
at  the  sill,  and  see  if  the  jambs  are  not  too  wide  for  the 
plaster;  if  they  are,  the  over-wood  must  be  sawn  or  planed 


PRACTICAL   CENTRING.  67 

off  until  they  come  flush  with  the  plaster.  Take  the  jambs 
down  when  this  is  done,  and  lay  out  a  ^4  in.  dado  from  the 
groove  mark.  This  dado  is  to  receive  the  foot-head.  Then 
take  the  foot-head,  cut  it  to  the  length  of  the  dados  of  the 
head,  and  %6  in.  for  a  tongue  on  each  end.  Work  these 
tongues  on  ^  in.  deep,  and  nip  the  foot-head  to  the  width 
of  the  jambs.  Ease  the  tongue  as  well  as  the  jambs,  and 
nail  the  head  side  and  foot-head  together  afterwards;  set 
them  up  in  their  place,  and  when  they  are  driven  home  toe- 
nail  them  into  the  casing. 

When  setting  door  jambs  on  underflooring,  or  where  the 
finishing  floor  is  not  yet  laid,  always  take  the  following 
precautions : 

First,  place  a  straight-edge  across  the  floor  to  each  stud 
at  each  opening  to  ascertain  if  the  weight  of  partition  has 
not  sunk  it  out  of  level. 

Second,  ask  the  foreman  if  there  are  base  blocks  on  the 
trim. 

Now  if  there  are,  base  blocks  and  the  base  must  be  kept 
level.  Supposing  one  opening  has  the  floor  sunk  a  ]/2  in. 
below  the  level,  and  another  i  in.  below,  the  difficulty  will 
be  to  set  the  jambs  so  that  each  base  block  will  be  level  with 
the  other,  and  the  door  heads  their  proper  height  and  level. 
In  such  a  case  proceed  as  follows: 

The  height  of  the  doors  being  determined  by  one  8'  6" 
clear  of  head  and  floor  and  one  9'  6",  nail  the  heads  and 
jambs  together  and  tack  a  piece  across  the  edges  of  the 
jambs  about  12  in.  from  the  bottom,  equally  distant  from 
the  head,  about  f  6"  down,  and  keep  the  jambs  parallel 
by  marking  the  piece  with  the  pencil  equal  to  the  inside 
distance  at  the  head.  This  being  done,  obtain  a  10  ft. 
rod  and  lay  off  8'  7%"  for  the  8'  6"  jambs,  and  mark  this 
length  on  one  edge  of  each  jamb.  This  mark  will  be 
the  scribe  line  for  the  jambs,  or  their  exact  length. 
Set  them  in  the  opening  between  the  studs,  and  place 
a  true  level  on  the  strip,  and  wedge  up  the  lowest  side 
until  the  bulb  is  exactly  in  the  centre.  Now  set  your  com- 
passes to  the  line  on  the  stile  resting  on  the  floor,  and  keep- 


68  PRACTICAL   CENTRING. 

ing  the  jambs  about  plumb,  scribe  them  to  the  floor;  saw 
these  lines,  always  leaving  the  line  on,  and  replace  the 
jambs  far  out  from  the  studs,  and  nail  them  perfectly 
plumb  and  straight  on  the  face.  Be  sure  they  are  perfectly 
straight,  and  wedge  out  all  short  crooks  and  lumps.  There 
is  too  much  careless  jamb-setting  just  now,  and  one  has 
only  to  fit  a  few  doors  to  find  this  out.  Also  keep  them 
square  to  the  edges,  and  be  sure  they  are  not  nailed  in  wind. 

The  object  of  nailing  on  the  strip  is,  that  by  tacking  it 
on  equally  distant  from  the  head  and  levelling  it  the  head 
is  likewise  levelled  without  the  trouble  of  climbing  upon  a 
horse.  The  *^  in.  being  added  to  the  length  brings  the 
head  up  ^  in.  higher,  so  that  the  base  will  come  level  with 
the  top  of  the  base  block  on  the  trim. 

The  9'  6"  jambs  are  set  in  the  same  way,  except  that  i  in. 
is  allowed  9'  8"  instead  of  l/2  in.  The  extra  one  inch  on  the 
length  is  8'  7",  9"  7'  is  to  allow  for  the  finishing  floor  i  in. 
thick.  This  method  should  always  be  followed  for  first- 
class  trim  when  there  is  a  supervising  architect  who  uses 
his  eyes.  In  trimming  doors,  the  trim  now  comes  to  the 
building  put  together,  or  with  the  stiles  and  head  casing 
glued  and  do  welled  perfectly  square,  fitted  and  varnished 
or  polished,  all  ready  to  nail  up ;  so  it  is  absolutely  necessary 
that  the  jambs  be  properly  set  and  their  edges  levelled  to 
insure  the  joints  being  close. 

Jambs  should  never  be  set  too  wide  for  the  thickness  of 
the  wall,  as  in  a  great  many  cases  no  wall  moulding  is 
employed,  and  the  back  joints  must  fit  to  the  plaster. 
They  must  also  be  out  of  wind.  In  nailing  on  trim  care 
should  be  taken  to  have  the  margin  on  the  edge  showing 
equal  all  round,  for  it  often  occurs  that  the  trim  may  be 
put  together,  and  -^  in.  more  or  less  than  the  dimensions 
shown  on  the  details;  therefore,  if  only  a  y&  in.  is  shown 
on  the  stiles,  the  same  must  be  left  on  the  head.  One 
thing  in  particular  must  be  well  done — namely,  to  fur  well 
under  the  back  edges  of  all  casings  and  corner  blocks,  and 
to  fit  the  wall  mould  close,  as  the  recesses  left  by  careless- 
ness in  this  respect  are  too  often  the  abodes  of  vermin. 


CHAPTER  XIV. 

WORKING    HARDWOOD    AND    CLAMPING. 

r"PHE  following  information  may  prove  useful  to  those 
carpenters  who  have  never  worked  hardwood,  and 
who  may  be  suddenly  given  a  job  to  do.  When  nailing, 
never  drive  cut- iron  nails  without  first  boring  for  them.  A 
German  bit  is  the  best  to  use ;  they  cut  clean  and  easy,  and 
pull  out  the  cores.  Wire  nails,  however,  are  best  for  the 
work,  and  if  the  wood  be  very  hard,  as  heart  ash  or  quar- 
tered oak,  the  point  should  be  dipped  in  wax  or  soap.  A 
very  convenient  grease-box  can  be  made  by  boring  a  ^  in. 
hole  in  the  haft  of  a  hammer,  and  filling  it  up  with  wax  or 
soap;  it  is  always  at  hand,  and  not  in  the  way.  When 
nailing  in  panel  moulding,  never  drive  the  nail  so  slanting 
that  it  will  go  into  the  panel,  but  keep  it  nearly  parallel 
with  the  face  of  the  panel,  so  that  the  nail  will  enter  the 
•edge  of  the  stile  rail  or  muntin.  By  driving  it  thus,  it  will 
hold  the  moulding  on  the  frame ;  but  if  it  goes  into  the 
panel,  when  the  panel  shrinks  the  moulding  will  draw 
away  from  the  edge,  and  likely  split  the  panel. 

When  possible,  nail  all  work  so  that  the  nail-holes  will 
cover.  For  instance,  when  setting  jamts  nail  through  the 
edges  into  the  studding,  as  polished  or  varnished  work 
showing  the  natural  wood  is  marred  by  nailing  through  the 
face.  If  it  must  be  nailed  on  the  face  as  trimming,  be 
very  careful  not  to  split  the  work,  and  use  a  small  pointed 
set.  Be  sure  there  is  no  grease  left  on  the  face  of  the 
hammer  after  each  nail  is  driven,  because  it  is  liable  to 
bend  the  next  nail.  The  best  way  to  make  inside  joints 
with  hardwood  is  to  scribe  them.  Often  the  stuff  is 
warped,  and  cutting  a  square  joint  only  means  fitting, 


70  PRACTICAL   CENTRING. 

which  can  be  avoided  by  scribing  the  joint.  If  it  is  com- 
pulsory to  nail  back  .a  piece  of  very  much  twisted  stuff,  like 
hazel  or  sycamore,  the  mechanic  should  be  very  cautious, 
for  kiln -dried  timber  is  so  brittle  and  non-elastic  that  it  will 
not  readily  yield  to  strain  and  will  crack  like  glass.  The 
best  plane  to  use  on  all  hardwood  is  of  course  the  iron 
plane,  especially  where  the  wood  is  curly  or  cross-grained. 
Keep  the  plane  sharp  and  keen.  Dull  tools  may  do  fairly 
well  on  pine,  but  on  hardwood  they  are  useless ;  so  keen 
edges  are  indispensable  for  clean  work,  so  that  little  scrap- 
ing need  be  done.  A  good  iron  block  plane  is  also  neces- 
sary, but  I  would  recommend  all  cuts  and  mitres  to  be 
made  direct  from  the  saw.  A  good  workman  will  make 
his  calculations  carefully,  and  insure  the  certainty  of  his 
cut  before  making  it. 

Finally,  proceed  carefully  and  steadily,  and  don't  bang 
the  work  with  the  hammer.  Use  a  block  if  you  must  drive 
the  stuff,  so  as  not  to  mark  it,  and  make  a  good,  clean  job. 

CLAMPING. 

How  many  men  are  there  in  our  carpenter  shops  nowa- 
days who  can  systematically  and  perfectly  glue  and  clamp 
up  a  stub-tenon  door?  There  are  very  few  indeed,  and  a. 
great  many  faulty  joints  can  be  attributed  to  the  very  want 
of  this  necessary  knowledge.  Clamping,  especially  in  the 
case  of  hardwood  or  veneered  doors,  shutters,  etc. ,  should 
be  done  rapidly  and  perfectly,  in  order  that  the  glue  may 
be  enabled  by  the  auxiliary  means  employed  to  assist  its- 
operation  to  properly  perform  its  function.  The  usual 
method  employed  is  to  take  the  framed  door  apart,  place 
the  stiles  together  face  to  face,  and  put  them,  mortised 
edge  down,  in  the  hot  box.  Similarly,  all  the  rails  and 
mortises  are  heated  to  the  same  temperature  as  the  hot  box. 
When  heated,  the  stiles  are  first  taken  out,  the  mortised 
edges  turned  up,  and  the  mortises  are  smeared  inside  with 
glue  (moderately  thick),  also  the  relishes  and  shoulders. 
The  mortises  for  muntins  in  the  rails,  or  in  the  muntins, 
if  there  be  any,  are  also  smeared,  then  the  tenons  and  tusks. 


PRACTICAL   CENTRING.  71 

Put  in  the  bottom  rail  first,  face  side  to  face  side  of  stile, 
keeping  the  face  edge  to  laying-out  mark  on  stile;  then 
slip  in  your  panel,  if  it  goes  in  without  any  fillet,  and 
insert  the  muntin  in  bottom  rail  mortise.  Drive  in  all  the 
rails  and  muntins  in  this  manner,  and  when  all  are  in,  turn 
the  whole  upside  down,  and,  inserting  the  other  tenons  in 
the  second  stile,  slam  the  door  down  on  the  bench  to  bring 
the  shoulders  to  their  place.  Drop  the  door  on  the  clamps,, 
and  quickly  give  all  the  clamps  a  turn  to  squeeze  out  the 
glue.  Slack  them  back  again,  and  adjust  a  tail  clamp 
lengthways  over  the  muntins.  Place  the  muntins  exactly 
to  the  laying-out  mark,  and  squeeze  them  to  tighten  joints 
on  the  rails.  Keep  the  rails  perfectly  square  to  the  stiles,, 
or  the  joints  will  never  hold,  and  screw  the  clamps  hard,, 
carefully  watching  that  the  joints  do  not  spring  up  or  start 
the  veneer,  also  that  the  door  does  not  wind  or  raise  up 
from  the  clamps.  Expedition  and  a  little  care  will  insure 
a  good  job,  and  the  latent  heat  in  the  wood  will  keep  the 
glue  from  setting  until  the  parts  are  together. 


CHAPTER  XV. 

EXTEMPORIZED    SCAFFOLDING. 

T)UILDERS  throughout  the  country  in  their  daily  prac- 
f)  tice  find  it  necessary  to  erect  temporary  scaffolding, 
and  in  doing  so  usually  employ  scrap  stuff,  or  some  of  the 
material  they  intend  using  in  the  building.  These  scaffolds 
require  to  be  handy,  take  little  time  in  constructing,  and 
must  at  the  same  time  be  strong  and  suitable  for  safely  sus- 
taining men  and  material.  With  a  view  to  assist  builders 
to  a  rapidly  formed  system  of  scaffolding  the  following  is 
submitted : 

The  handiest,  though  not  always  the  most  applicable 
form,  is  the  bracket  scaffold,  which  consists  of  a  number  of 
permanently  framed  -timber  brackets,  placed  on  a  line,  at  a 
convenient  distance  apart,  on  which  to  rest  the  planks. 
Each  bracket  measures  about  4  X  4  ft. ,  and  is  framed  together 
of  \y2  in.  or  2X3  in-  sound  spruce,  for  lightness  and 
strength.  It  is  held,  in  its  place  on  the  frame  wall  by  a 
y±  in.  round  iron  bolt,  which  is  forged  long  enough  to  pass 
through  the  boarding  and  studding,  and  a  2  in.  block, 
which  spans  two  studs  inside.  The  end  of  the  bolt  is  tapped, 
and  the  bracket  can  be  screwed  tight  against  the  board- 
ing by  a  screw,  key  and  washer.  The  bolt  is  fastened  to 
the  bracket  under  the  horizontal  arm,  after  passing  through 
a  hole  in  the  vertical  arm,  by  being  forged  flat  and  bored 
and  bolted  to  it  with  y±  in.  bolts,  which  are  countersunk  on 
the  upper  side  of  the  arm,  to  permit  the  plank  to  rest  level 
on  it. 

All  that  is  required  to  affix  these  brackets  to  the  building 
is  to  bore  a  hole  for  the  bolt,  and  they  hang  quite  safe,  and 
will  sustain  the  weight  of  any  ordinary  quantity  of  boards 


PRACTICAL   CENTRING.  73 

or  siding.  They  can  also  be  put  up  for  boarding,  and 
taken  down  as  each  strip  of  covering  is  finished. 

In  the  absence  of  the  above,  a  good  safe  scaffold  can  be 
quickly  made  of  joists  and  i/%  in.  covering  or  roofing 
boards.  Cleats  gained  out  the  thickness  of  the  bracket 
board  are  first  got  out,  and  to  the  gain  a  bracket  piece  is 
well  nailed;  the  outer  end  of  the  bracket  piece  is  next 
nailed  square  to  the  side  of  a  sound  joist  at  the  required 
height,  and  the  three  together  are  then  nailed  by  the  cleat 
through  the  wall  boarding  into  a  stud.  If  much  weight  is 
to  be  put  on  the  scaffold,  blocks  should  be  nailed  under  the 
bracket  piece  on  the  vertical  joist  to  take  the  strain  off  the 
nails,  especially  when  hemlock  joists  are  used  for  uprights. 

A  very  simple  way  of  gaining  a  strong  scaffold  is  to  lay 
joists  on  their  edges  across  brackets  no  more  than  ten  feet 
apart,  with  ledgers  placed  across  their  upper  edges,  on  which 
the  planks  rest.  It  is  also  very  convenient  when  the  scaf- 
folding planks  are  not  forthcoming,  and  boards  are  substi- 
tuted, and  it  saves  a  double  thickness  of  boards.  This  scaf- 
fold is  braced  diagonally,  and,  in  order  to  increase  its  height, 
another  joist  can  be  placed  on  the  top  end  of  the  bottom 
one,  and  the  joist  secured  by  nailing  a  y%  cleat  across  it. 

A  useful  and  easily  removed  scaffold  for  putting  on  roof 
boarding  consists  of  simple  brackets  nailed  through  the 
roof  boarding  into  the  rafters  beneath,  with  a  plank  laid 
.across  them  to  stand  on. 

When  the  boarding  is  all  on,  and  the  window  frames  and 
cornice  set,  one  of  the  next  accessories  is  a  handy  shin- 
gling stage.  After  the  first  courses  have  been  laid,  it  is 
usual  to  form  a  scaffold  out  of  joist  laid  against  the  roof  on 
their  edge,  and  fastened  by  shingles.  The  best  way,  how- 
ever, is  to  shingle  the  joist  in,  by  nailing  the  shingles  to 
it,  and  fastening  them  in  a  course  of  shingles,  keeping 
those  nailed  on  the  joist  down,  so  that  the  joist  will  come 
below  the  butts  of  those  in  the  course.  These  can  be  cut 
off  when  the  scaffold  is  no  longer  needed,  and  the  roof  will 
not  have  been  in  any  way  injured. 

The  handiest  scaffold  which  a  carpenter  and  builder  can 


74  PRACTICAL   CENTRING. 

adopt  for  setting  cornices  over  store  fronts,  consists  of  a 
piece  of  8  or  9  by  i  in.  spruce  board  nailed  square  across 
near  the  ends  of  two  joists  at  the  desired  height,  far  enough 
apart  to  permit  each  joist  to  stand  respectively,  allowing 
for  the  difference  in  their  levels  on  the  store  floor  and  side- 
walk. When  the  number  of  these  frames  needed  is  nailed 
together,  they  are  placed  in  position,  braced  diagonally, 
and  the  plank  laid  across  them.  This  method  makes  a 
very  convenient,  firm  scaffold,  and  costs  very  little  time. 


CHAPTER  XVI. 

HINTS    AND    SUGGESTIONS. 

"T^OREMAN  carpenters  should  have  a  boy  or  two  on  the- 
•         works.     They  are  very  handy  for  running  errands, 
picking  up  stuff,  etc. 

If  possible,  keep  all  your  scaffolding  plant  in  stock  and  in 
good  order.  Do  not  waste  time  on  improvised  scaffolds, 
unless  they  can't  possibly  be  avoided. 

Builders  should  be  careful  to  see  that  their  masons,  when 
building  chimneys  in  frame  structures,  do  not  sustain  any 
part  of  the  brickwork  on  the  timber  construction,  because 
all  brickwork  settles  to  a  more  or  less  extent,  and  should 
the  whole  weight  of  a  chimney-stack  be  brought  to  bear  on 
lower  floor  beams,  it  will  surely  bear  it  down  and  throw  it 
out  of  level. 

When  lumber  is  placed  adjacent  to  the  side  of  a  prospect- 
ive building,  always  see  that  it  is  stacked  so  that  the  air  will 
circulate  round  each  piece  and  season  it  thoroughly.  Fram- 
ing pieces  should  be  regularly  built  up  in  level  piles,  with, 
strips  between  each  stick  or  layer  of  sticks.  Boards,  as 
flooring,  sheathing,  siding  or  clapboarding,  should  be 
stacked  in  triangular  stacks  or  kept  in  extemporized  sheds. 
They  should  never  be  allowed  to  twist  or  warp,  or  be  ex- 
posed to  the  sun's  rays  or  rain. 

When  laying  rough  floor,  or  under  floor,  in  good  work, 
if  double  floors  are  used,  always  lay  it  diagonally,  as  it  will 
be  found  more  economical  for  the  following  reasons :  First, 
when  the  finished  floor  is  laid  it  liesevener;  second,  it  is 
easier  laying  the  finished  floor  because  the  under  floor  does 
not  prevent  it  from  driving  together  through  the  uneven- 
ness  of  the  joints;  third,  it  binds  the  building  stronger 


76  PRACTICAL  -CENTRING. 

together ;  and  fourth,  trie  time  seemingly  lost  is  more  than 
made  up  in  the  rapidity  in  which  the  finished  floor  can  be 
laid  on  top  of  it. 

When  raising  the  frames  of  buildings,  especially  those  of 
the  balloon  type,  it  is  absolutely  necessary  to  brace  them 
thoroughly  in  order  that  the  pieces  which  are  already  in 
position  may  not* be  jarred  or  strained  out  of  place  while 
raising  the  other  pieces  which  rest  on  them.  To  illustrate 
this,  I  might  say  that  when  the  side  walls  are  up  they  must 
be  well  stayed  by  board  braces,  nailed  on  diagonally  at 
•each  end,  to  the  sills  and  posts.  It  is  likewise  a  judicious 
practice  to  rough-board  or  cover  the  outside  walls  before 
raising  the  roof,  and,  when  possible,  this  boarding  will  be 
much  better  if  nailed  on  diagonally.  Some  maintain  that 
the  horizontal  boarding  is  sufficient,  and  makes  a  house 
strong  enough  to  resist  any  ordinary  wind  pressure ;  but  the 
first  method  not  alone  makes  a  stiffer  construction,  but 
gives  a  smoother  surface  for  laying  on  the  clapboarding  or 
siding. 

When  finished  stuff  comes  to  a  building  ready  to  be  put 
up,  there  is  often  much  carelessness  displayed  in  placing  it 
so  as  to  preserve  its  form  and  finish.  It  would  be  admir- 
able if  builders  and  foremen  would  consider  its  cost  and 
future  more  and  place  it  safely  in  its  proper  position.  For 
this  reason  we  put  forward  the  following,  which  our  friends 
who  are  builders  will,  no  doubt,  recognize  as  judicious: 
No  inside  finish  should  be  brought  to  a  job  until  it  is  fully 
plastered  and  ready  to  have  it  put  up.  When  the  base 
comes,  as  it  is  kiln-dried,  it  should  be  stacked  up  with  thin 
strips  between  each  board  to  allow  the  air  to  circulate  and 
keep  it  as  dry  as  possible  in  the  damp  building.  All  the 
joined  trim  and  doors  should  be  brought  to  a  job  as  soon  as 
possible,  in  order  that  it  may  become  seasoned  as  the  build- 
ing dries  out,  especially  the  doors,  because  they  are  more 
liable  to  absorb  the  dampness  inherent  in  every  newly  plas- 
tered building.  In  fact,  they  will  absorb  a  certain  amount 
and  swell  to  a  large  extent.  They  should  not  be  fitted 
while  in  this  condition,  but  left  until  the  walls  are  dried  out ;. 


PRACTICAL   CENTRING.  77 

so  that  when  they  do  shrink  after  fitting,  the  shrinkage 
will  be  reduced  to  a  minimum.  Framed  work  of  all  kinds 
should  therefore  be  stacked  vertically  against  a  wall,  to 
obviate  the  danger  of  twisting,  or  laid  flat,  one  on  top  of 
another,  with  strips  between  each  piece  and  weighted. 
A  good  plan  is  to  shore  them  down  solid  from  the  ceiling 
or  opposite  wall.  Another  preventive  often  used  is  to 
first  give  the  stuff  a  coat  of  oil  filler,  or  priming  coat  of 
paint,  which  has  the  good  quality  of  filling  up  the  open 
pores  of  the  kiln-dried  material  and  to  a  large  extent  pre- 
venting the  absorption  mentioned  above.  Veneered  work 
should  also  be  carefully  guarded,  and  precautions  taken  to 
counteract  the  effect  of  the  prevalent  moisture  so  destruc- 
tive to  finely  finished  work.  Varnished  work  should  be 
filled  and  polished  work  oiled. 

I  note  that  many  builders  are  partial  to  setting  their  door 
and  window  jambs  before  the  plaster  is  put  on,  thus  making 
their  edges  grounds,  as  it  were,  to  straighten  the  plaster 
surfaces.  This  practice  is,  to  my  mind,  a  mistake,  and 
some  of  its  consequences  show  this.  Plaster  should  always 
be  put  on  to  grounds  nailed  on  the  studding,  and  not  to  the 
edges  of  finished  work. 

If  you  are  not  already  able  to  draw  or  lay  out  a  piece  of 
work  full  working  size  from  an  architect's  drawing,  I 
would  recommend  you  to  learn  how  to  do  it  right  away. 
No  man  can  do  a  job  as  it  ought  to  be  done  unless  he  under- 
stands the  idea  the  architect  intends  to  convey  by  his  scale 
drawing.  Another  pointer  is  this:  Don't  jump  to  the  con- 
clusion that  the  architect's  detail  is  wrong  because  you 
can't  work  from  it.  I  have  found  that  there  are  many 
men  who,  as  long  as  things  are  clear  to  them,  are  all 
right,  but  the  moment  anything  arises  which  seems  com- 
plicated or  difficult,  they  will  not  stop  to  solve  it,  but 
rush  off  to  the  architect,  complaining  that  such,  and  such 
a  thing  wont  work  out.  If  you  can't  understand  it  at  first, 
lay  it  aside  for  a  while,  and  when  you  have  leisure,  as  at 
noon  hour,  quietly  think  it  out.  Then  if  it  wont  work 
itself  out,  see  the  architect  and  have  it  fully  explained. 


78  PRACTICAL   CENTRING. 

Be  sure,  when  putting  on  siding,  that  the  courses  are 
straight  right  through,  especially  when  they  are  long,  or 
over  1 5  ft.  from  casing  to  casing,  or  corner  board  to  casing, 
or  corner  board  to  corner  board.  Let  me  suggest  to  all 
who  are  conscientious  that  they  nail  into  the  studs  and 
not  through  the  sheathing,  as  water  will  surely  go  through 
and  rot  both  siding  and  boards. 

I  see  a  good  many  men  using  a  level  to  plumb  their 
posts  and  studding  with.  This  looks  all  right,  but  it  isn't 
the  proper  way.  The  proper  way  is  to  use  a  good  plumb 
rule,  as  long  as  can  be  handled,  with  a  heavy  lead  bob  on 
it.  By  this  means,  if  the  post  be  lumpy  on  the  surface  or 
not  quite  straight,  the  long  straight-edge  of  the  rule  will 
more  likely  keep  it  correct  than  a  short  level  two  or  two 
and  one-half  feet  long.  This  applies  also  to  levelling  sills. 
Don't  place  the  level  right  on  the  sill,  but  use  a  long, 
parallel  straight-edge,  and  block  up  the  sill  until  it  touches 
the  edge  right  through. 

I  know  of  no  quality  so  essential  to  make  a  successful 
mechanic  as  self-confidence,  and  this  as  a  rule  only  comes 
from  ability.  I  would  therefore  recommend  all  carpenters 
to  become  as  expert  as  possible. 

Allow  me  to  warn  carpenters  against  the  indiscriminate 
use  of  the  claw  on  the  hammer.  When  you  have  to  pull  a 
bent  or  broken  nail  out  in  nailing  up  trim  or  finish  of  any 
kind,  don't  take  a  leverage  with  the  head  directly  on  the 
smooth  surface  of  the  stuff,  but  place  a  block  under  the 
head.  It  gives  more  leverage,  prevents  the  surface  being 
bruised,  and  likewise  shows  a  careful  workman. 

Mortise  locks  ought  never  to  be  set  into  the  door  stile 
too  tight,  because  when  they  don't  fit  easy  the  plates  are 
pressed  inward  and  the  movable  parts  inside  are  jammed 
and  turn  hard.  A  ^  in.  mortise  lock  ought  therefore  to 
be  bored  for  with  a  ^  in.  auger  bit,  ^  in.  with  a  ^  in.,  and 
so  on.  The  mortise  should  be  cut  straight  with  the  sur- 
faces parallel  to  the  faces  of  the  door  stile,  in  order  that  the 
edges  of  the  face  plate  may  likewise  be  parallel  to  the  arrises 
formed  by  the  junction  of  the  faces  and  edge. 


PRACTICAL    CENTRING.  79 

Let  me  give  builders  a  pointer  about  floors  which  they 
should  remember.  Don't  lay  your  finish  floors  till  all  the 
mechanics  are  out  of  the  house,  and  when  they  are  laid 
cover  them  carefully  with  paper.  Another  one  is :  Always 
keep  your  stairs  covered  with  paper  and  boards  until  the 
job  is  finished,  as  it  is  a  pity  to  see  hardwood  treads  all 
scratched  up,  which  will,  of  course,  show  through  the 
finish. 

When  you  are  fitting  doors  don't  make  the  top  joint  too 
•close,  for  in  a  new  job  the  walls  will  settle  down,  and  they 
can't  be  opened.  Always  cut  the  stiles  on  pine  doors  about 
jig-  in.  short,  so  that  when  the  top  rail  shrinks  it  will  come 
back  flush  with  the  ends  of  the  stiles.  If  you  have  to  bend, 
base,  or  chair-rail  around  corners,  kerf  it  from  the  back, 
and  do  it  systematically  by  spacing  the  kerfs  equally,  in  or- 
der that  the  piece  will  bend  without  breaking.  I  used  to 
wet  my  stuff,  which  made  it  more  flexible  and  yielding,  and 
when  nailing  it  on  I  either  shored  or  bracketed  it  in  from 
opposite  wall  or  floor. 

As  I  see  the  use  of  the  saddle  or  threshold  on  inside  doors 
is  going  out  of  date,  in  order  to  allow  the  carpet  to  pass 
from  one  room,  to  another  without  having  to  cut  it,  I  would 
recommend  that  when  you  are  fitting  doors  that  you  leave 
the  bottom  edge  of  the  outside  corner  an  eighth  of  an  inch 
shorter  than  the  hanging  side  corner. 

There  are  many  men  who  express  different  opinions 
about  iron  and  wood  planes.  Now,  as  far  as  my  experience 
goes,  and  it  extends  over  many  years'  continuous  work,  I 
think  the  iron  plane  is  good  on  ash,  oak,  maple,  sycamore, 
cherry,  butternut,  satinwood,  rosewood,  mahogany,  wal- 
nut, etc.,  as,  being  always  close  in  the  mouth  and  capable 
of  being  finely  set  on  the  edge,  it  lessens  the  danger  of 
tearing  out  the  grain,  which  is  so  great  in  open-mouthed 
wooden  planes ;  but  they  must  be  nicely  set  and  handled, 
or  they  leave  a  mark  which  will  incur  much  labor  to  take 
out  with  scraper.  Here  I  would  say  a  word  about  scrapers, 
as  opinions  about  sharpening  these  tools  differ  somewhat. 
Some  say  the  only  way  to  sharpen  a  scraper  is  to  file  the 


80  PRACTICAL   CENTRING. 

edge  perfectly  straight  and  square  to  the  sides,  and  then 
turn  up  the  arris  with  a  smooth  file  or  round  side  of  a 
gauge.  This  is  a  very  good  way,  but  a  better  one,  I  think, 
is  to  grind  the  edge  with  a  basil  like  a  plane  iron  and  whet 
it  upon  an  oil-stone  till  it  lifts  a  shaving  like  a  plane  iron 
or  bit.  I  used  to  use  a  wood  stock  on  my  scraper,  to  save 
my  hand  from  getting  blistered  or  raw  when  I  had  much 
scraping  to  do. 

A  very  good  method  to  bend  such  trimming  stuff  as  chair 
rail,  base,  necking,  etc.,  is  to  place  the  piece  in  water  over 
night.  This  makes  it  soft  and  easily  bent,  so  it  can  be 
turned  into  simple  or  compound  curves  of  any  radius. 
This  also  helps  when  kerfing  stuff  round  curves,  as  it 
tends  to  make  the  wood  more  elastic. 

Sycamore  and  hazel  base  will  need  to  have  wood  plugs 
driven  in  the  joints  of  the  brick,  and  vertical  strips,  the 
thickness  of  the  plaster,  nailed  on,  to  hold  it  securely  in 
position. 

I  cannot  recommend  the  method  of  fastening  mantels  to 
chimney  breasts  by  nailing  a  strip  to  the  brickwork  under 
the  shelf.  A  better  method  would  be  to  plug  and  then  nail 
the  strip  to  the  plugs,  but  care  must  be  taken  to  drive  no- 
wood  into  the  flues. 


